# The best AgentMail alternatives (2026) Seven AgentMail alternatives for platforms, compared on per-inbox pricing, catch-all domains, users' Gmail and Outlook, opt-out replies and outreach rules. [Pau Kraft](https://paukraft.com) Founder, AI Inbx · [@paukraft on X](https://x.com/paukraft) 5 November 2026 · 18 min read Updated 6 November 2026 TL;DR In my view, AgentMail is made for personal assistants (it is the [official email plugin for OpenClaw](https://www.agentmail.to/build/openclaw)): its model works for one person's own agent with no backend in between. For a product that gives its own customers or agents email, I think AI Inbx is the better alternative: - **Every address works.** AI Inbx accepts mail for any address on a verified domain with nothing created, and bills by email. AgentMail needs an inbox per address, with no catch-all, and on its paid plans each inbox past the plan is $2 a month. More - **Your users' Gmail and Outlook.** AI Inbx connects them to the same API as your domains. AgentMail's docs describe no way to connect an existing mailbox. More - **Replies read for you.** On AI Inbx a reply without reply headers stays on its thread, answers typed inside the quote are kept, out-of-office return dates and verification codes arrive as fields, and attachments arrive as text, scanned pages included. More - **Outreach allowed, with rules.** AgentMail does not support cold outreach. AI Inbx allows what the recipient's law permits, with pacing, sending hours and opt-out replies suppressed for you. More - **A bill that doesn't grow with customers.** For 500 addresses and 50,000 emails a month, AI Inbx comes to $49 and AgentMail to $900. More - **Built for volume.** The agent reads only what's new and automated mail needs no model call, so the work per email stays small, with up to 1,000 pacing rules on Growth and no limit on Scale. More AgentMail is the better pick when each agent needs IMAP and SMTP, or you need a free plan and a SOC 2 report (when to stay). Nuntly and Sendmux (now Qubrics) cost less than AI Inbx in the worked bill. The row-by-row case against AgentMail is in [AI Inbx vs AgentMail](/blog/ai-inbx-vs-agentmail). *I'm Pau, and I founded AI Inbx, so I'm not neutral, but I believe I've portrayed each provider fairly, including where it's the better pick. Everything said here about AgentMail and the other products is from their public docs, terms and pricing pages as of November 2026, linked where it's used. If something is wrong or out of date, email me and I'll fix it.* I have been on the other side of this choice. Before AI Inbx I built agent systems that run in production for enterprises in the sourcing industry, thousands of emails a month, and every provider I tried left the same papercuts to my code: threading that broke on edge cases, opt-outs buried in reply text, mail going out at hours no person would send it. The alternatives below are judged by how many of those they take off your hands. Ours comes first, then Nylas and Resend, which added hosted mailboxes this year, then the agent-inbox, testing and sending services. ## How the seven compare | Product | What it's for | | --- | --- | | AgentMail (for reference) | An inbox per agent, created through the API | | AI Inbx | Sending and receiving for products: every address on your domains, plus your users' Gmail and Outlook | | Nylas | Email on users' Google, Microsoft, Exchange and IMAP accounts, plus Agent Accounts | | Resend | Developer email API with receiving, Inboxes, templates and Broadcasts | | OpenMail | An inbox per agent, through an API, CLI or MCP server | | MailSlurp | Test inboxes, SMS numbers and mailbox connectors | | Nuntly | Transactional sending and inbound inboxes | | Sendmux (now Qubrics) | Outbound through your own Gmail, Outlook and SMTP accounts, plus agent mailboxes | The rows where AI Inbx and AgentMail differ come first, then the ones where they match, then each plan's pricing and free tier. Every cell links to the page it comes from. | Feature | AI Inbx | AgentMail | Nylas | Resend | OpenMail | MailSlurp | Nuntly | Sendmux | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Receiving | | **Threads that hold without reply headers** Replies join their conversation even when they arrive without reply headers: a colleague answering from another address, a client that drops them, a changed subject. Partial: threads are grouped by reply headers, or by the mailbox provider's own threading, and nothing more is documented. | **Yes** Every email belongs to a thread, including replies that arrive without reply headers, from a colleague's address or under a changed subject; threads are listed, read and replied to through the API. Replies join their conversation even when a client mangles or drops the reply headers, a colleague answers from another address or the subject changes; a shared subject alone never merges two conversations. [1](https://docs.aiinbx.com/guides/threads) [2](https://docs.aiinbx.com/guides/receiving#threading) [3](https://aiinbx.com/features/threading) | **Partial** Threads are created automatically and can be listed, searched and read per inbox, per pod or across the organization. Replies without reply headers are not described as joining their thread. [1](https://docs.agentmail.to/threads) [2](https://docs.agentmail.to/knowledge-base/threaded-conversations) | **Partial** For Google and Microsoft accounts the Threads API returns the provider's own Gmail threads and Outlook conversations; Nylas groups IMAP mail itself, and Agent Account replies are linked by In-Reply-To and References, with replies without those headers not described. [1](https://developer.nylas.com/docs/v3/email/threads/) [2](https://developer.nylas.com/docs/v3/agent-accounts/email-threading/) | **Partial** Inboxes (announced 2026-10-22) group emails sent and received in reply to each other into threads that can be listed, searched and replied to; the Chat SDK adapter threads by Message-ID, In-Reply-To and References, and replies without those headers are not described. [1](https://resend.com/docs/guides/inboxes/threads) [2](https://resend.com/blog/announcing-inboxes) [3](https://resend.com/docs/chat-sdk) | **Partial** Threading matches In-Reply-To and References against earlier Message-IDs, and the docs state that a message with no match starts a new thread; threads can be listed per inbox and read in order. [1](https://docs.openmail.sh/concepts/threading) | **Partial** GET /emails/threads lists conversation threads inferred from Message-ID, In-Reply-To and References, and GET /emails/threads/{threadId}/items returns their messages. Replies without reply headers are not described as joining their thread. [1](https://api.mailslurp.com/v2/api-docs/) [2](https://www.mailslurp.com/llms.txt) | **Partial** Messages are grouped into threads by In-Reply-To and References; without a matching header, a message joins a thread in the same inbox whose normalised subject matches and that had activity in the last 7 days, otherwise a new thread starts. [1](https://nuntly.com/docs/guides/receiving-threads) | **Partial** The Mailbox API lists conversation threads and their messages, which carry in\_reply\_to and references; how replies without reply headers are grouped is not described. [1](https://sendmux.ai/docs/developer-tools/mailbox-api/threads) [2](https://sendmux.ai/docs/api/mailbox-api/list-mailbox-threads) [3](https://app.sendmux.ai/api/v1/openapi.json) | | **Reply text, inline answers kept** Each inbound message comes with the newly written text separated from quoted history and signatures, and answers typed inside the quote are kept. Partial: the quote is removed or marked, but answers inside it are not kept or not documented as kept. | **Yes** Each email carries stripped\_text and stripped\_html without the quoted conversation, keeping answers typed inline into the quote, and segments marking written, quoted and signature parts; a sender's signature is kept the first time they use it in a thread. stripped\_text keeps answers typed into the quote next to the lines they answer, also when the mail client leaves the quote unmarked, as long as the answered message is on the thread. [1](https://docs.aiinbx.com/guides/receiving#what-was-written) [2](https://aiinbx.com/solutions/email-reply-parser) | **Partial** Every message has extracted\_text and extracted\_html without quoted history and trailing boilerplate; the sender's own signature is kept. When the sender answers between quoted lines, extracted\_text keeps the message whole so the answers are not lost; extracted\_html still cuts at the first quote. [1](https://docs.agentmail.to/reply-extraction) | **Partial** Clean Conversations (PUT /messages/clean or the message.created.cleaned webhook) removes reply and forward content and signatures and returns the latest message; Nylas calls the cleaning heuristic, and whether answers typed inside the quote are kept is not described. [1](https://developer.nylas.com/docs/v3/email/parse-messages/) [2](https://developer.nylas.com/docs/cookbook/email/clean-messages/) [3](https://developer.nylas.com/docs/reference/notifications/messages/message-created-cleaned/) | **No** The documented received-email and thread-email objects carry the full html and text bodies, with no field for the newly written text apart from the quoted history. [1](https://resend.com/docs/api-reference/emails/retrieve-received-email) [2](https://resend.com/docs/api-reference/inboxes/get-thread-email) | **Partial** The MCP server's read\_thread tool strips quoted reply history, while the API and webhook fields carry the full body; whether answers typed inside the quote are kept is not described. [1](https://docs.openmail.sh/integrations/mcp) [2](https://docs.openmail.sh/pages/webhooks/events) [3](https://api.openmail.sh/openapi.json) | **Not documented** The email schema has body, bodyExcerpt and textExcerpt fields; a field with the new text separated from quoted history is not documented. [1](https://api.mailslurp.com/v2/api-docs/) | **Not documented** Message content is served as HTML, plain-text or raw MIME download links; a field with quoted history and signatures removed is not documented. [1](https://nuntly.com/docs/guides/receiving-messages) [2](https://nuntly.com/docs/api-reference/messages/retrieve-message-content) | **Partial** The clean content endpoint strips quoted replies and signatures by default (strip\_quotes, strip\_signature); whether answers typed inside a quote are kept is not documented. [1](https://sendmux.ai/docs/developer-tools/mailbox-api/message-content) | | **Out-of-office with return date** Out-of-office and other automatic replies are flagged on the message, with the day the sender is back and the colleague they name as fields. Partial: automatic replies are flagged, without those details. | **Yes** Every inbound email has a category such as human, out\_of\_office or auto\_reply, and an away reply carries the reason, return day and named contacts when it states them. An out\_of\_office or auto\_reply email carries unavailable with the reason (absent, left or unmonitored), back\_on for the first day back and the contacts the reply names, each when the reply states it. [1](https://docs.aiinbx.com/guides/receiving#categories) [2](https://aiinbx.com/solutions/auto-reply-detection) [3](https://docs.aiinbx.com/guides/receiving#what-automated-mail-asks-for) | **Not documented** The docs and message schema do not mention flagging out-of-office or other automatic replies. [1](https://docs.agentmail.to/api-reference/inboxes/messages/get) [2](https://docs.agentmail.to/events) | **Partial** Automated replies to mail sent through Nylas are reported on Google and Microsoft grants as a message.bounce\_detected event with type automated\_reply, not a flag on the message, and Nylas states that detection doesn't extract return dates. [1](https://developer.nylas.com/docs/v3/email/send-email/) | **No** The documented received-email, thread-email and inbox.email.received objects have no field marking out-of-office or other automatic replies; the raw headers are returned. [1](https://resend.com/docs/api-reference/emails/retrieve-received-email) [2](https://resend.com/docs/webhooks/inboxes/email-received) | **Partial** Each inbound message has a category (personal, automated, marketing, bounce, spam or malicious) and an auto\_replyable flag; the documented fields include no return date or alternative contact. [1](https://docs.openmail.sh/pages/webhooks/events) [2](https://api.openmail.sh/openapi.json) | **Not documented** The docs and email schema do not mention flagging out-of-office or other automatic replies. [1](https://api.mailslurp.com/v2/api-docs/) [2](https://www.mailslurp.com/docs/emails/) | **Not documented** Received messages carry security and spam checks; flagging of out-of-office or other automatic replies is not documented. [1](https://nuntly.com/docs/guides/receiving-messages) [2](https://nuntly.com/docs/guides/receiving-webhooks) | **Not documented** Flagging of out-of-office or other automatic replies is not documented. [1](https://sendmux.ai/docs/developer-tools/mailbox-api/message-content) [2](https://sendmux.ai/docs/webhooks/setup) | | **Verification codes as fields** A verification email comes with its one-time code or confirmation link as fields on the message. | **Yes** A verification email carries verification.code and verification.link, both written in the email, on the email and its email.received event. [1](https://docs.aiinbx.com/guides/receiving#what-automated-mail-asks-for) | **No** The documented Get Message response has no field for a code or confirmation link; with AgentID, an assistant reads the verification email itself or signs the agent in without one. [1](https://docs.agentmail.to/api-reference/inboxes/messages/get) [2](https://docs.agentmail.to/agentid-in-assistants) | **Partial** The Nylas CLI's otp get and otp watch commands return a 6-digit code found in recent mail; API messages carry no code field, and Nylas's Agent Account recipe extracts codes in your own code with regex and an LLM fallback. [1](https://developer.nylas.com/docs/cookbook/cli/extract-otp-codes/) [2](https://developer.nylas.com/docs/cookbook/agent-accounts/extract-otp-code/) | **No** The documented received-email and thread-email objects have no fields for one-time codes or confirmation links. [1](https://resend.com/docs/api-reference/emails/retrieve-received-email) [2](https://resend.com/docs/api-reference/inboxes/get-thread-email) | **No** The documented message.received fields and Message schema include no field for a one-time code or confirmation link; the MCP server's list\_unread\_threads tool filters out OTP mail as machine-generated. [1](https://docs.openmail.sh/pages/webhooks/events) [2](https://api.openmail.sh/openapi.json) [3](https://docs.openmail.sh/integrations/mcp) | **Partial** POST /emails/{emailId}/codes extracts one-time codes on request (pattern, LLM or OCR) and returns the best code with ranked candidates, and GET /emails/{emailId}/links lists the links in an email; the email object itself carries no code field. [1](https://api.mailslurp.com/v2/api-docs/) [2](https://www.mailslurp.com/docs/emails/) | **No** The documented message fields (sender, recipients, subject, status, labels, attachment count, raw headers) include no field for a one-time code or confirmation link. [1](https://nuntly.com/docs/guides/receiving-messages) [2](https://nuntly.com/openapi.json) | **No** The OpenAPI message and clean content schemas list every field (no additional properties); extracted\_links returns the body's links, and no field holds a one-time code or marks a confirmation link. [1](https://app.sendmux.ai/api/v1/openapi.json) [2](https://sendmux.ai/docs/developer-tools/mailbox-api/message-content) | | **Attachments as text, scans included** PDFs, documents and spreadsheets arrive with their content as text or Markdown, ready for an LLM, and scanned or image-only PDF pages are read too. Partial: text is extracted only from a PDF's text layer, only for some file types, or only on a separate request. | **Yes** PDFs, documents and spreadsheets come with prepared Markdown or text; scanned pages are read too and count against a monthly page allowance. [1](https://docs.aiinbx.com/guides/attachments) [2](https://docs.aiinbx.com/guides/billing#advanced-attachment-processing) | **Partial** Get Attachment returns a text\_url with text extracted from PDF, Word, Excel and text files up to 10 MB; PDF text comes from the text layer only, and the docs say scanned or image-only PDFs have no text. [1](https://docs.agentmail.to/reply-extraction) | **No** Attachments download as raw bytes; Nylas's own recipe passes PDFs and images to your model to extract their content. [1](https://developer.nylas.com/docs/cookbook/email/parse-email-attachments/) | **No** Received attachments come as metadata plus a download\_url valid for 1 hour, from which your app downloads the content; extracted text is not among the documented fields. [1](https://resend.com/docs/dashboard/receiving/attachments) | **Partial** Inbound attachments carry parsedText from PDFs, Office documents, CSV, text files and images, including scanned documents sent as images (OCR), up to 10 MB per file and 50,000 characters; reading scanned pages inside a PDF is not described. [1](https://docs.openmail.sh/concepts/attachments) | **Partial** Text is extracted on a separate request to POST /attachments/{attachmentId}/text, with AUTO, NATIVE (text, Word, spreadsheets, PDFs with embedded text), OCR or LLM methods; it does not arrive with the email. [1](https://api.mailslurp.com/v2/api-docs/) [2](https://www.mailslurp.com/docs/ai-transformers/) | **Not documented** Attachments come with metadata and a temporary download URL; extracting their content as text is not documented. [1](https://nuntly.com/docs/api-reference/messages/list-message-attachments) [2](https://nuntly.com/docs/api-reference/messages/retrieve-message-attachment) | **Partial** A separate request extracts an attachment of up to 7.5 MB as Markdown text at no extra charge; OCR is unavailable, so scanned pages are not read. [1](https://sendmux.ai/docs/developer-tools/mailbox-api/message-content) [2](https://sendmux.ai/docs/api/mailbox-api/request-attachment-text) | | Mailboxes | | **Any address on a domain** Mail to any address on a receiving domain is accepted without creating each address first. | **Yes** Once the inbound MX record resolves, mail to any address on the domain is accepted, plus addresses such as reply+ord\_8812@ included, with nothing registered per address. [1](https://docs.aiinbx.com/guides/receiving#receiving-on-a-domain) | **No** AgentMail's blog states it does not offer catch-all; each receiving address needs an inbox. [1](https://www.agentmail.to/blog/catch-all-vs-inbox-per-agent) [2](https://docs.agentmail.to/google-workspace) | **Not documented** Agent Accounts are created per address; the docs don't say what happens to mail for an address on the domain with no Agent Account. [1](https://developer.nylas.com/docs/v3/agent-accounts/provisioning/) | **Yes** Once the MX record is added, Resend receives email for any address at the domain. [1](https://resend.com/docs/dashboard/receiving/introduction) | **No** Mail a verified custom domain accepts for an address with no inbox is dropped and recorded as inbound\_rejected\_no\_inbox in the policy audit log. [1](https://docs.openmail.sh/api-reference/policy/list-correspondent-policy-audit-events) [2](https://api.openmail.sh/openapi.json) | **Yes** Each custom domain gets a catch-all inbox that receives mail not addressed to a specific inbox on the domain. [1](https://www.mailslurp.com/docs/custom-domains/) | **Yes** Enabling receiving creates a default catch-all inbox (\`\*\`) that takes mail for every address without its own inbox. [1](https://nuntly.com/docs/guides/receiving-inboxes) | **No** A catch-all mailbox is listed as a planned domain control; for now each address needs its own mailbox. [1](https://sendmux.ai/docs/domains/settings) | | **Subdomains for each customer** Each of your customers can get their own subdomain to send and receive on, without them editing DNS. | **Yes** After one wildcard domain such as \*.saas.com is verified, each customer's subdomain is created through the API with no DNS of its own, and can be placed in that customer's space. [1](https://docs.aiinbx.com/guides/domains#wildcards-and-subdomains) [2](https://aiinbx.com/features/wildcard-domains) | **Yes** With subdomains\_enabled and one wildcard MX record on a parent domain, inboxes can be created on any subdomain; they share the parent domain's DKIM key and sending identity. [1](https://docs.agentmail.to/knowledge-base/subdomain-inboxes) [2](https://www.agentmail.to/blog/custom-domains-for-thousands-of-agent-inboxes) | **Partial** Each customer subdomain is registered as its own domain with MX and TXT records that you publish, and plans include 1 (Essentials), 10 (Pro) or 20 (Pro annual) custom sending domains; nylas.email trial subdomains need no DNS and are documented for prototyping and demos. [1](https://developer.nylas.com/docs/v3/agent-accounts/dns-provider-setup/) [2](https://developer.nylas.com/docs/v3/agent-accounts/provisioning/) [3](https://www.nylas.com/pricing/) | **Partial** Subdomains can be added through the Domains API, but each is added and verified individually with its own DNS records and counts toward the plan's domain limit. [1](https://resend.com/docs/dashboard/domains/introduction) [2](https://resend.com/docs/knowledge-base/setting-up-resend-for-multi-tenants) | **Partial** A custom domain, which can be a subdomain, can be scoped to one customer's pod; each domain is added and verified with its own DNS records. [1](https://docs.openmail.sh/concepts/pods) [2](https://docs.openmail.sh/concepts/custom-domains) | **Not documented** The custom domain docs describe verifying domains you control; giving each customer a provider-managed subdomain is not documented. [1](https://www.mailslurp.com/docs/custom-domains/) | **Not documented** Each organization gets one receiving-only provided subdomain at sign-up; giving each of your customers a subdomain without DNS edits is not documented. [1](https://nuntly.com/docs/guides/ai-agents) [2](https://nuntly.com/docs/api-reference/inboxes/create-inbox) | **Not documented** Addresses on the shared myagent.mx domain need no DNS; per-customer subdomains without DNS edits are not documented. [1](https://sendmux.ai/docs/domains) | | **Connect users' Gmail** Read and send from a user's existing Gmail or Google Workspace mailbox after they grant access. | **Yes** Users connect Gmail or Google Workspace over OAuth through your own Google OAuth app, from a hosted page, a link or the API; mail syncs in and can be sent as the account and its Send-as aliases. [1](https://docs.aiinbx.com/guides/mailboxes) [2](https://aiinbx.com/features/mailboxes) | **No** AgentMail gives each agent its own inbox; its docs describe no way to connect an existing Gmail or Google Workspace mailbox. [1](https://docs.agentmail.to/knowledge-base/what-is-agentmail) [2](https://www.agentmail.to/blog/best-email-api-for-ai-agents-2026) | **Yes** A Google connector lets users grant OAuth access to Gmail. [1](https://developer.nylas.com/docs/provider-guides/google/) | **No** Inboxes live on your own verified domains; an existing mailbox can be forwarded into an inbox, and no Google account connection is documented. [1](https://resend.com/docs/guides/inboxes/create-inboxes) | **No** OpenMail gives each agent a dedicated inbox it hosts, not a shared mailbox; connecting an existing Gmail account is not part of the product (an inbox can forward copies to Gmail). [1](https://openmail.sh/llms.txt) [2](https://api.openmail.sh/openapi.json) | **Yes** Connectors sync a Gmail or Google Workspace mailbox into a MailSlurp inbox and send through it; the connector docs use IMAP and SMTP with an app password, and the agent guide also names Google OAuth. [1](https://www.mailslurp.com/docs/connectors/) [2](https://www.mailslurp.com/docs/agents/) | **No** Nuntly sends and receives on domains you verify with it, and receives on a subdomain it provides (built on AWS SES); connecting a user's existing Gmail mailbox is outside that scope. [1](https://nuntly.com/llms.txt) [2](https://nuntly.com/docs/guides/receiving-overview) | **Partial** Gmail and Google Workspace accounts connect as sending accounts with the gmail.send scope only; reading their mail is not requested. [1](https://sendmux.ai/docs/sending/accounts/google-microsoft) | | **Connect users' Outlook** Read and send from a user's existing Outlook or Microsoft 365 mailbox after they grant access. | **Yes** Users connect Outlook or Microsoft 365 over OAuth through your own Microsoft Entra app, from a hosted page, a link or the API; mail syncs in and can be sent as the account. [1](https://docs.aiinbx.com/guides/mailboxes) [2](https://aiinbx.com/features/mailboxes) | **No** AgentMail gives each agent its own inbox; its docs describe no way to connect an existing Outlook or Microsoft 365 mailbox. [1](https://docs.agentmail.to/knowledge-base/what-is-agentmail) [2](https://www.agentmail.to/blog/best-email-api-for-ai-agents-2026) | **Yes** The Microsoft connector covers Microsoft 365, Exchange Online, Exchange Server 2003+ and personal Outlook.com accounts, and an EWS connector covers Exchange on-prem. [1](https://developer.nylas.com/docs/provider-guides/microsoft/) [2](https://developer.nylas.com/docs/provider-guides/exchange-on-prem/) | **No** Inboxes live on your own verified domains; an existing mailbox can be forwarded into an inbox, and no Microsoft account connection is documented. [1](https://resend.com/docs/guides/inboxes/create-inboxes) | **No** OpenMail gives each agent a dedicated inbox it hosts, not a shared mailbox; connecting an existing Outlook account is not part of the product. [1](https://openmail.sh/llms.txt) | **Yes** Connectors sync an Outlook or Microsoft 365 mailbox over IMAP and SMTP (outlook.office365.com) with a password or app password and send through it. [1](https://www.mailslurp.com/docs/connectors/) [2](https://www.mailslurp.com/docs/agents/) | **No** Nuntly sends and receives on domains you verify with it, and receives on a subdomain it provides (built on AWS SES); connecting a user's existing Outlook mailbox is outside that scope. [1](https://nuntly.com/llms.txt) [2](https://nuntly.com/docs/guides/receiving-overview) | **Partial** Outlook and Microsoft 365 accounts connect as sending accounts with Mail.Send only; reading their mail is not requested. [1](https://sendmux.ai/docs/sending/accounts/google-microsoft) | | **IMAP and SMTP** Connect mailboxes over IMAP, or send and read through SMTP/IMAP credentials. | **No** AI Inbx is an HTTP API with no SMTP relay, and mailboxes connect over Google and Microsoft OAuth, not IMAP. [1](https://aiinbx.com/solutions/send-email-api) [2](https://docs.aiinbx.com/guides/mailboxes) | **Yes** AgentMail inboxes can be read over IMAP and sent from over SMTP, with the inbox address as username and an API key as password. [1](https://docs.agentmail.to/imap-smtp) | **Yes** Connected IMAP accounts are read over IMAP and sent through SMTP, and Agent Accounts can be opened in mail clients over IMAP and SMTP submission on paid plans. [1](https://developer.nylas.com/docs/provider-guides/imap/) [2](https://developer.nylas.com/docs/v3/agent-accounts/mail-clients/) | **Partial** An SMTP relay (smtp.resend.com) is available for sending; IMAP access is not documented. [1](https://resend.com/docs/send-with-smtp) | **No** Not in the API reference: access is through the REST API, webhooks, WebSocket, CLI and MCP server, with no IMAP or SMTP access listed. [1](https://openmail.sh/llms.txt) [2](https://api.openmail.sh/openapi.json) | **Yes** Inboxes have IMAP and SMTP credentials for mail clients and libraries, and connectors link external mailboxes over IMAP and SMTP. [1](https://www.mailslurp.com/docs/imap-smtp/) [2](https://www.mailslurp.com/docs/connectors/) | **Partial** An SMTP relay on port 587 is available for sending; received mail is read through the API and webhooks, and IMAP access is not documented. [1](https://nuntly.com/docs/guides/send-emails-with-smtp) [2](https://nuntly.com/docs/guides/receiving-overview) [3](https://nuntly.com/rfc/imap) | **Yes** Each mailbox password works for IMAP retrieval and SMTP submission, and custom SMTP accounts can be added as sending providers. [1](https://sendmux.ai/docs/mailboxes) [2](https://sendmux.ai/docs/sending/smtp) [3](https://sendmux.ai/docs/sending/accounts) | | Sending | | **Configurable send limits** You set limits such as N per hour per sending address or per recipient domain, and the provider holds mail back to keep to them. | **Yes** Limit rules cap sends per rolling window for the rule, each sending address, sending domain, recipient or recipient domain, and hold the rest until there is room; plans set how many active rules a workspace holds. [1](https://docs.aiinbx.com/guides/pacing#rate-limits) [2](https://aiinbx.com/features/pacing) | **Not documented** Docs describe plan send limits per day and per 5 minutes and a warm-up schedule to follow yourself; limits you set per address or recipient domain are not documented. [1](https://docs.agentmail.to/knowledge-base/rate-limits) [2](https://docs.agentmail.to/email-deliverability) | **Partial** For Agent Accounts a policy sets a daily send quota per account, and sends over it return HTTP 429 rather than being held; connected mailboxes follow their provider's limits. [1](https://developer.nylas.com/docs/v3/agent-accounts/policies-rules-lists/) [2](https://developer.nylas.com/docs/v3/agent-accounts/send-limits/) | **Not documented** Resend documents its own API rate limit (10 requests per second per team by default) and plan quotas; limits you set per address or recipient domain are not documented. [1](https://resend.com/docs/api-reference/rate-limit) | **Not documented** OpenMail applies its own per-inbox burst limit (10/minute) and a new-recipient cap and rejects sends over them with a 429; limits you set yourself are not documented, and Enterprise caps are negotiated with OpenMail. [1](https://docs.openmail.sh/concepts/rate-limits) | **Not documented** A sending queue retries emails when the account hits temporary limits; customer-set limits per hour, sender or recipient domain are not documented. [1](https://www.mailslurp.com/docs/emails/) | **Partial** The Broadcast docs say delivery is paced by Nuntly; limits you set yourself per sender or recipient domain are not documented. [1](https://nuntly.com/docs/guides/broadcast-overview) [2](https://nuntly.com/docs/api-reference/rate-limits) | **Yes** Your own sending accounts take per-second, per-minute, per-hour and per-day quotas, and mail over an account's cap is held; the managed Amazon SES account's quotas cannot be edited. [1](https://sendmux.ai/docs/use-cases/cold-email-outreach) [2](https://sendmux.ai/docs/sending/accounts) | | **Sending hours** You set the hours mail may go out, for example weekdays 9–17 in a timezone, and mail outside them waits. | **Yes** Hours rules set weekly sending windows in an IANA timezone, optionally opening and closing at a varying minute each day; mail outside them waits. [1](https://docs.aiinbx.com/guides/pacing#sending-hours) [2](https://aiinbx.com/features/sending-hours) | **Not documented** Docs suggest sending drafts at a chosen time with send\_at; account-wide sending hours are not documented. [1](https://docs.agentmail.to/drafts) | **Not documented** The docs describe per-message send\_at scheduling; no setting for allowed sending hours was found. [1](https://developer.nylas.com/docs/v3/email/scheduled-send/) | **Not documented** Individual emails can be scheduled for a time; a setting for allowed sending hours is not documented. [1](https://resend.com/docs/dashboard/emails/schedule-email) | **No** Not in the API reference: the send endpoint has no scheduling field and no sending-window setting is listed, so mail goes out when it is sent. [1](https://docs.openmail.sh/concepts/rate-limits) [2](https://docs.openmail.sh/api-reference/messages/send-email) | **Not documented** Individual emails can be scheduled; a setting for allowed sending hours is not documented. [1](https://www.mailslurp.com/docs/emails/) | **Not documented** Sending windows are not documented; individual emails can be timed with scheduledAt. [1](https://nuntly.com/docs/api-reference/emails/send-email) | **Not documented** Sending windows by time of day are not documented. [1](https://sendmux.ai/docs/sending/accounts) | | **Suppression lists** Addresses that bounced, complained or unsubscribed are blocked from later sends, manageable through the API. | **Yes** Bounces that show an address is dead, complaints and unsubscribes (link, one-click or a reply asking to stop) are suppressed automatically, on named lists per campaign and per space, managed through the API. [1](https://docs.aiinbx.com/guides/suppressions) [2](https://aiinbx.com/features/suppressions) | **Yes** Sends to addresses that bounced, were rejected or complained are blocked automatically, and send block lists at organization, pod or inbox level are managed through the Lists API. [1](https://docs.agentmail.to/knowledge-base/emails-bouncing) [2](https://docs.agentmail.to/lists) | **No** Nylas states it doesn't ship suppression lists and its bounce guide says to add permanently failed addresses to your own; Agent Account outbound block rules with address Lists can stop sends to addresses you add. [1](https://developer.nylas.com/docs/cookbook/email/sendgrid-alternative/) [2](https://developer.nylas.com/docs/v3/agent-accounts/policies-rules-lists/) [3](https://developer.nylas.com/docs/cookbook/use-cases/build/handle-bounced-email/) | **Yes** Hard bounces and complaints are suppressed automatically team-wide, and suppressions can be listed, added and removed through the API; unsubscribes are handled per contact and topic for Broadcasts. [1](https://resend.com/docs/dashboard/emails/email-suppressions) [2](https://resend.com/docs/dashboard/contacts/managing-unsubscribe-list) | **Partial** Hard bounces, spam complaints and one-click unsubscribes are suppressed automatically and later sends return 422 recipient\_suppressed; the docs list no suppression endpoints, and lifting an unsubscribe goes through support. [1](https://docs.openmail.sh/concepts/suppressions) | **Yes** Bounced and unsubscribed recipients cannot be emailed again and are listed through the API; rulesets block or filter recipients when sending. [1](https://api.mailslurp.com/v2/api-docs/) | **Partial** Permanent bounces and spam complaints go on a suppression list automatically; reviewing or removing an address is done by contacting support. [1](https://nuntly.com/docs/guides/broadcast-unsubscribe) | **Not documented** A suppression list kept by Sendmux is not documented; the cold outreach guide asks senders to honour their own suppression records. [1](https://sendmux.ai/docs/use-cases/cold-email-outreach) [2](https://sendmux.ai/docs/monitoring/deliverability) | | **Opt-out replies suppressed** A reply asking not to be emailed again is recognised and the address is suppressed without your code reading it. | **Yes** A reply asking to stop is recognised as an opt-out and suppressed automatically, reported as email.unsubscribed with source reply. [1](https://docs.aiinbx.com/guides/suppressions#reacting-to-the-events) [2](https://docs.aiinbx.com/webhooks/events/email-unsubscribed) | **No** The docs tell you to read a reply's extracted\_text to decide whether it is an opt-out and then add the address to the send block list yourself. [1](https://docs.agentmail.to/knowledge-base/cold-outreach) [2](https://docs.agentmail.to/knowledge-base/account-suspended) | **No** Nylas states it doesn't ship unsubscribe handling or suppression lists. [1](https://developer.nylas.com/docs/cookbook/email/sendgrid-alternative/) | **Not documented** Suppressions come from bounces, complaints and manual additions, and Broadcast unsubscribes from Resend's unsubscribe link; recognising an opt-out written in a reply is not described. [1](https://resend.com/docs/dashboard/emails/email-suppressions) [2](https://resend.com/docs/dashboard/contacts/managing-unsubscribe-list) | **Not documented** Suppression is documented for hard bounces, spam complaints and one-click unsubscribes; opt-outs written in a reply are not described. [1](https://docs.openmail.sh/concepts/suppressions) | **Not documented** Bounced and List-Unsubscribe recipients are blocked from further sends; recognising an opt-out written in a reply is not documented. [1](https://api.mailslurp.com/v2/api-docs/) | **Not documented** The docs add addresses to the suppression list on permanent bounces and spam complaints and handle Broadcast unsubscribe links; recognising an opt-out written in a reply is not documented. [1](https://nuntly.com/docs/guides/broadcast-unsubscribe) | **Not documented** Recognising opt-out requests in replies is not documented; the cold outreach guide asks senders to settle their own suppression and opt-out handling. [1](https://sendmux.ai/docs/use-cases/cold-email-outreach) | | Platform | | **Separation per customer** Your customers' domains, mailboxes and settings are kept apart inside one account (sub-accounts, pods, spaces or similar). | **Yes** Spaces keep each customer's domains, mailboxes, mail, pacing rules, suppression lists and sending reputation apart inside one workspace; API keys and webhook endpoints are workspace-wide. [1](https://docs.aiinbx.com/guides/spaces) [2](https://aiinbx.com/features/spaces) | **Yes** Pods isolate each customer's inboxes, domains, threads and drafts, with pod-scoped API keys and webhooks; Terms §4(c) make integrating into your own app subject to your subscription tier, and §8(l) forbid making API keys or account credentials available to any third party. [1](https://docs.agentmail.to/documentation/core-concepts/pods) [2](https://docs.agentmail.to/multi-tenancy) [3](https://www.agentmail.to/legal/terms) | **Yes** Workspaces group an application's grants per customer organization, and for Agent Accounts carry the policy and rules (Agent Account workspace isolation is not on the Free plan). [1](https://developer.nylas.com/docs/dev-guide/platform/workspaces/) [2](https://developer.nylas.com/docs/v3/agent-accounts/workspaces/) [3](https://www.nylas.com/pricing/) | **Partial** Resend's multi-tenant guide uses one account with domain-scoped API keys and tags, or a separate Resend team per customer; per-tenant analytics are not available natively and teams cannot be created through the API. [1](https://resend.com/docs/knowledge-base/setting-up-resend-for-multi-tenants) [2](https://resend.com/docs/dashboard/settings/team) | **Yes** Pods are isolated sub-accounts, addressable by your own clientId, that hold a tenant's inboxes and scoped domains, with pod-scoped API keys; unlimited on every plan. [1](https://docs.openmail.sh/concepts/pods) [2](https://openmail.sh/pricing) | **Partial** Environments give one organization separate workspaces with their own inboxes, domains, API keys and webhooks; the pricing page lists isolated environments under Enterprise. [1](https://www.mailslurp.com/docs/environments/) [2](https://app.mailslurp.com/pricing/) | **Partial** Namespaces group and isolate inboxes per tenant, mapped to your own externalId, on Starter and above; in the API reference, domains, webhooks and API keys carry no namespace. [1](https://nuntly.com/docs/guides/receiving-namespaces) [2](https://nuntly.com/pricing.md) [3](https://nuntly.com/openapi.json) | **Yes** One team per customer isolates mailboxes, providers, delivery logs, billing and API keys; each Pro team costs $7 a month plus usage. [1](https://sendmux.ai/solutions/platform-builders/) [2](https://sendmux.ai/docs/account/teams-and-access) | | **Sending reputation per customer** Each of your customers' sending reputation is kept apart, so one customer's bounces or complaints don't pause another's mail. | **Yes** Each space sends on its own reputation: bounces and complaints count against the space the mail left from, and a space over the line is paused by itself; mailbox providers still judge every subdomain of one wildcard as that one domain. [1](https://docs.aiinbx.com/guides/spaces#one-reputation-per-space) [2](https://docs.aiinbx.com/concepts#space) | **Partial** AgentMail can suspend a single inbox or pod while the rest of the account keeps sending, but it weighs bounce and complaint signals across the organization's mail and can also suspend the whole account. [1](https://docs.agentmail.to/knowledge-base/account-suspended) | **Yes** Nylas tracks bounce and complaint rates and pauses sending per sending domain, and documents one Agent Account per customer on the customer's own domain with its own sender reputation; connected mailboxes send through each user's own provider. [1](https://developer.nylas.com/docs/v3/agent-accounts/send-limits/) [2](https://developer.nylas.com/docs/v3/agent-accounts/) [3](https://developer.nylas.com/docs/cookbook/email/choosing-an-email-api/) | **Partial** Resend's multi-tenant guide says tenants in one account share its sender reputation and one tenant's poor sending can affect all of them; independent reputation takes a separate Resend account per tenant. [1](https://resend.com/docs/knowledge-base/setting-up-resend-for-multi-tenants) | **Yes** Reputation is tracked per inbox and per domain, and the reputation engine suspends a single inbox or pod without affecting the whole account; the account-wide cold-outreach cap is shared across pods. [1](https://docs.openmail.sh/pages/webhooks/events) [2](https://docs.openmail.sh/concepts/rate-limits) [3](https://docs.openmail.sh/best-practices/email-deliverability) | **Not documented** The API reports SES tenant sending and reputation status per MailSlurp user; whether environments or other resources within one account keep separate sending reputation is not documented. [1](https://api.mailslurp.com/v2/api-docs/) [2](https://www.mailslurp.com/docs/environments/) | **Not documented** The docs say high bounce or complaint rates may lead to suspension of the sending domain or account and keep one suppression list per organization; keeping each customer's reputation apart is not documented. [1](https://nuntly.com/docs/guides/observability-sending) [2](https://nuntly.com/docs/guides/broadcast-unsubscribe) | **Not documented** Teams separate each customer's mailboxes, providers, logs and billing; whether bounces and complaints on managed sending are counted or acted on per team is not documented. [1](https://sendmux.ai/docs/account/teams-and-access) [2](https://sendmux.ai/docs/monitoring/deliverability) | | **SOC 2 report** A SOC 2 Type II report is available to customers. | **No** No SOC 2 report is published; the DPA offers security documentation, questionnaire responses and one customer audit a year. [1](https://aiinbx.com/dpa#assistance) | **Yes** AgentMail completed a SOC 2 Type II audit in 2025; the report is shared through its Trust Center after access approval, and the pricing page lists it on Startup and Enterprise. [1](https://docs.agentmail.to/documentation/resources/security-privacy/soc-2-compliance) [2](https://www.agentmail.to/pricing) | **Yes** The SOC 2 Type II report is available under NDA to current and prospective customers through the Nylas Trust Center. [1](https://www.nylas.com/security/) | **Yes** Resend is SOC 2 Type II compliant, and the report can be downloaded from the Documents page in the dashboard. [1](https://resend.com/docs/security) | **Not documented** The pricing page, docs and terms do not mention a SOC 2 report. [1](https://openmail.sh/pricing) [2](https://openmail.sh/terms) | **Partial** The trust centre lists SOC 2 Type 1 as compliant, and Enterprise includes SOC 2 documentation for security reviews; a Type II report is not listed. [1](https://trust.inc/pettman-o) [2](https://app.mailslurp.com/pricing/) | **Not documented** The site cites GDPR compliance; a SOC 2 report is not mentioned. [1](https://nuntly.com/README.md) [2](https://nuntly.com/pricing.md) | **No** Asked whether it is SOC 2 or otherwise certified, the enterprise page says Sendmux is not certified against a specific standard yet and that certifications are on its roadmap. [1](https://sendmux.ai/solutions/enterprise/) | | Policy | | **No charge per address** The price doesn't depend on how many addresses, inboxes or mailboxes you use; it follows email volume or a flat fee. | **Yes** Price follows emails per month; addresses are never counted or charged. Developer ($5/month) caps custom domains at 50 and connected mailboxes at 100; both are unlimited from Growth ($29/month). [1](https://aiinbx.com/pricing) [2](https://docs.aiinbx.com/guides/billing#domains-mailboxes-and-pacing-rules) | **No** Plans include 3, 10 or 150 inboxes, and on Developer and Startup each extra inbox is a $2/month add-on. [1](https://www.agentmail.to/pricing) | **No** Plans include a set number of connected accounts and Agent Accounts, and each additional connected account is charged (+$2.25 per account on Essentials, +$2.00 on Pro monthly). [1](https://www.nylas.com/pricing/) | **No** Every plan includes 3 inboxes and paid plans add more at $1 per inbox per month; sending and plain receiving on a verified domain are priced by email volume. [1](https://resend.com/pricing) | **No** Free has 3 inboxes as a hard cap; Pro includes 10 inboxes and then bills €1 per extra inbox per month. [1](https://openmail.sh/pricing) | **No** Each plan includes a number of inboxes created per month (100 to 5,000) and inboxes kept (250 on Starter), and on Pro and Growth extra inboxes are billed at usage rates. [1](https://app.mailslurp.com/pricing/) | **Partial** Plans are priced by monthly email volume and include 1, 10, 100 or unlimited inboxes; the pricing page lists no charge per extra inbox. [1](https://nuntly.com/pricing.md) [2](https://nuntly.com/pricing) | **Partial** No per-seat or per-mailbox fees, but each isolated customer is its own team at $7 a month on Pro, on top of usage billed per event; Free holds 2 mailboxes. [1](https://sendmux.ai/pricing/) | | **Cold outreach allowed** The terms or acceptable use policy allow sending unsolicited B2B outreach, within the law. | **Yes** The Acceptable Use Policy allows marketing email that the applicable law permits and bans unlawful unsolicited email, stating that a public address, a scraped list or legitimate interest alone is not permission. [1](https://aiinbx.com/acceptable-use#permission) [2](https://aiinbx.com/use-cases/cold-outreach) | **No** The docs state AgentMail does not support cold outreach, and Terms §8(h) prohibit unsolicited email. [1](https://docs.agentmail.to/knowledge-base/cold-outreach) [2](https://www.agentmail.to/legal/terms) | **Partial** The Terms of Use bar sending 'any unsolicited or unauthorized advertising, promotional materials, email ... or other form of solicitation', while the Agent Accounts docs list a sales agent that 'runs cold outreach campaigns' as a use case. [1](https://www.nylas.com/legal/terms/) [2](https://developer.nylas.com/docs/v3/agent-accounts/) | **No** The Acceptable Use Policy prohibits unsolicited messages of any kind, including cold outreach, purchased lists or scraped contact data. [1](https://resend.com/legal/acceptable-use) | **Yes** The terms allow individual, relevant B2B outreach without prior opt-in where lawful, from your own verified domain, to non-purchased business addresses, with opt-out and at most two follow-ups; a daily cap on new recipients applies. [1](https://openmail.sh/terms) [2](https://docs.openmail.sh/concepts/rate-limits) | **Yes** The acceptable use terms prohibit unsolicited communications in violation of applicable law and purchased, harvested or rented lists; lawful outreach is not prohibited. [1](https://www.mailslurp.com/full-terms-and-conditions/) | **No** The docs list cold outreach to prospects as not allowed, and the Terms of Service prohibit unsolicited bulk email and purchased or scraped lists. [1](https://nuntly.com/docs/guides/broadcast-overview) [2](https://nuntly.com/legal/terms-of-service) | **Yes** Cold outreach is a documented use case through your own Gmail, Outlook or SMTP accounts to prospects you may lawfully contact; the managed Amazon SES route is for transactional email only. [1](https://sendmux.ai/docs/use-cases/cold-email-outreach) [2](https://sendmux.ai/acceptable-use/) | | Pricing | | What you pay for | Monthly plans by emails per month, sent and received both counting; plans also set how many custom domains, managed mailboxes and active custom pacing rules a workspace holds, and an allowance of advanced attachment processing pages. | Monthly plans sized by inboxes, emails per month and custom domains; on Developer and Startup, add-ons cost $2/month per extra inbox, per extra domain and per 1,000 extra monthly sends, and $5/month per seat. | Monthly plan fee plus per-unit overage: connected accounts, Agent Accounts (per account), and Agent Account emails sent, storage and bandwidth. | Transactional plans scale with emails sent and received per month; marketing plans scale with contacts; inboxes beyond the 3 included are $1 per inbox per month. | A monthly plan plus usage: Pro includes 10 inboxes, 10,000 emails and 10 GB storage, then bills per extra inbox, email and GB; seats are not billed. | Monthly plans sized by emails received, inboxes created and inboxes kept per month, with allowances for device previews, placement tests, warmup and AI tokens; Pro and Growth bill extra usage at published rates, and phone numbers are billed separately. | Monthly email volume, priced in EUR tiers; inbox, domain and webhook caps step up with the plan. | Per event: $0.50 per 1,000 provider-accepted recipients through your own providers, $0.75 per 1,000 through managed sending, $0.50 per 1,000 inbound mailbox deliveries, $0.02 per GB-month of storage, plus $7 per team per month on Pro. No per-seat or per-mailbox fees. | | Free tier | No free plan: the pricing FAQ says Developer is $5 a month and includes 5,000 emails. | Free, $0/month, no credit card: 3 inboxes, 1 custom domain, 3,000 emails/month (100/day), 3 GB storage, 2 seats; the "Sent via AgentMail" footer is not removed on Free. | Free, $0/month: 5 connected accounts, 3 Agent Accounts, 3,000 Agent Account emails/month, 3 GB storage and bandwidth; no custom sending domains (Nylas trial domain), 20 sends per Agent Account per day, all limits hard caps. | Free: $0/mo, 3,000 emails/mo (sent and received) with a limit of 100 emails per day, 3 domains, 3 inboxes, 1 webhook endpoint; 1,000 marketing contacts. | Free, €0/month, no credit card: 3 inboxes (hard cap), 3,000 emails/month, 3 GB storage, addresses on OpenMail's shared domains only, up to 100 emails/day; Free emails end with a "Sent with OpenMail, email for agents." line. | Free, $0, no card, 1 user: 250 emails received/month, 100 inboxes created/month, temporary inboxes only, 200 MB storage; no external sending, phone numbers or custom domains. | EUR 0/month: 3,000 emails/month, 100 emails/day, 1 domain, 1 inbox, 1 webhook, 30-day data retention. | $0 per team per month: 2 mailboxes, 1 domain, 1 connected sending account, 1 webhook, 2 credentials, $1 usage credit, 50 provider-accepted recipients per UTC day (managed sending 2 per hour); outgoing messages get an "Email sent via Sendmux" footer. | | Cheapest plan | Developer: $5/month for 5,000 emails, 50 custom domains, 100 managed mailboxes, 100 active custom pacing rules and 100 advanced attachment processing pages a month. | Developer, $20/month: 10 inboxes, 10,000 emails/month (1,000/day, 100 per 5 minutes), 10 custom domains, 10 GB storage, 2 seats, email support. | Essentials, $15/month: 10 connected accounts (+$2.25 per additional account), 10 Agent Accounts, 10,000 Agent Account emails/month, 10 GB storage and bandwidth, 1 custom sending domain; Agent Account resources are hard-capped with no overage. | Pro: $20/mo for 50,000 emails/mo, no daily limit, 10 domains, 5 webhook endpoints, 3 inboxes; overage $0.90 per 1,000 emails. | Pro, €9/month + usage: 10 inboxes then €1/inbox/month, 10,000 emails/month then €0.001/email, 10 GB storage then €0.10/GB/month, unlimited custom domains, spend management, no OpenMail footer. | Starter, $19.99/month, 1 user, personal use: 2,500 emails received/month, 500 inboxes created/month, 250 inboxes kept, 500 MB storage; external sending not included, custom domains as a paid add-on. | Starter from EUR 10/month for 10,000 emails/month (EUR 16 for 50,000, EUR 28 for 100,000): no daily limit, 10 domains, 10 inboxes, 3 webhooks, 30-day retention. | Pro: $7 per team per month plus prepaid usage, with Unlimited\* resources (fair usage, increases need admin approval) and a managed-sending starting allowance of 1,000 accepted recipients per day. | | Other limits | Growth: $29/month for 30,000 emails, unlimited domains and mailboxes, 1,000 pacing rules, 500 pages. Scale: $99/month for 100,000 emails, unlimited domains, mailboxes and pacing rules, 2,000 pages. Extra usage is opt-in at $0.001 per email ($1 per 1,000) and $0.01 per advanced page, with optional monthly spending caps; without it, sending stops at the allowance while receiving continues. Every plan has every feature. Billing is monthly only, in USD excluding tax. The provided .aiinbx.app domain is capped at 100 emails a day. | Startup, $200/month: 150 inboxes, 150 custom domains, 15,000 emails/day (1,500 per 5 minutes) with no separate monthly cap, unlimited storage, 10 seats, SOC 2 report. Enterprise is custom: up to unlimited inboxes, usage-based pricing, BYO cloud, dedicated IPs, OIDC/SAML SSO. Docs state custom domains start on Developer, while the pricing page lists 1 on Free. | Pro is $49/month (or $43/month billed annually): 25 connected accounts (+$2.00, annual +$1.75 each), 50 Agent Accounts (+$0.40, annual +$0.20 each), 50,000 Agent Account emails/month (from +$0.80, annual +$0.70 per 1,000), 50 GB storage and 50 GB/month bandwidth, 10 custom sending domains (20 on annual). Agent Accounts are counted cumulatively per month, so accounts deleted mid-month still count. Agent Account sends share 5 requests per second per organization in production. Custom tracking domain needs the $2,400/year Accelerator Package (Pro Annual). Enterprise is custom. | Domains: Free 3, Pro 10, Scale 1,000; domains add-on $20/mo adds 100 domains on paid transactional plans. Additional inboxes $1/inbox/month on paid plans with pay-as-you-go; Free stops at 3. Every email sent or received through an inbox counts toward the transactional quota. Overage capped at 5x the monthly quota. API rate limit 10 requests per second per team by default, same on every plan. Self-serve plans are monthly only. | Docs list per-inbox send limits of 10/minute and 200/day (the pricing page lists no daily send limit on Pro) and a daily cap on new recipients: on Pro 20/day per inbox and 150/day per account during warm-up, custom-domain tiers from 20 to 100/day, account cap rising to at most 500/day. Inbox creation is limited to 100/day per account. Enterprise is custom: dedicated sending IPs, SSO, volume discounts, 1-hour SLA. | External sending starts on Pro, $69/month (1 user, commercial use): 500 external sends/month, 5,000 emails received, 1,000 inboxes created/month, no limit on inboxes kept, 1 GB. Growth, $199/month: 2 users, 5,000 inboxes created/month, 1 custom domain included, 5 GB. The emails-received allowance is shared across all inboxes. Enterprise adds SSO, SCIM, isolated environments and SOC 2 documentation. Prices shown in USD; the page also offers EUR. | Scale runs from EUR 68/month (100,000 emails) to EUR 625/month (1,500,000 emails) with 1,000 domains, 100 inboxes and 10 webhooks; Enterprise (2,000,000+ emails) is custom with unlimited inboxes. Storage is 1 GB per inbox below Enterprise. Dedicated IPs are an add-on on Scale and Enterprise. Namespaces start at Starter. | A team is the isolation boundary, so each isolated customer is its own $7/month Pro team. Every accepted To, CC and BCC recipient is billed. Enterprise is custom, with dedicated infrastructure and custom SLAs. | | Sources | [1](https://aiinbx.com/pricing) [2](https://docs.aiinbx.com/guides/billing) [3](https://docs.aiinbx.com/guides/domains#your-provided-domain) | [1](https://www.agentmail.to/pricing) [2](https://docs.agentmail.to/knowledge-base/rate-limits) [3](https://docs.agentmail.to/knowledge-base/change-plan-billing) | [1](https://www.nylas.com/pricing/) [2](https://developer.nylas.com/docs/v3/agent-accounts/send-limits/) | [1](https://resend.com/pricing) [2](https://resend.com/docs/knowledge-base/what-is-resend-pricing) [3](https://resend.com/docs/knowledge-base/how-to-add-more-domains) [4](https://resend.com/docs/knowledge-base/account-quotas-and-limits) [5](https://resend.com/docs/api-reference/rate-limit) | [1](https://openmail.sh/pricing) [2](https://docs.openmail.sh/concepts/rate-limits) [3](https://docs.openmail.sh/concepts/inboxes) | [1](https://app.mailslurp.com/pricing/) | [1](https://nuntly.com/pricing) [2](https://nuntly.com/pricing.md) | [1](https://sendmux.ai/pricing/) [2](https://sendmux.ai/docs/account/team-limits) [3](https://sendmux.ai/docs/sending/accounts) [4](https://sendmux.ai/solutions/platform-builders/) | Checked 6 November 2026 from each product's public docs and pricing. Spotted a mistake? Email [me@paukraft.com](mailto:me@paukraft.com). ## AI Inbx (ours) AI Inbx sends and receives email over one API, on domains you own and in your users' Gmail and Outlook inboxes. I think it's the strongest alternative for a platform because it reads the mail for you (what a reply says, what an automated reply asks for, what an attachment contains) and keeps each customer's sending inside its own rules. ### Addresses, mailboxes and customers - AI Inbx accepts mail for every address on a verified domain with nothing created: `reply+ord_8812@mail.yourapp.com` receives as soon as the MX record resolves. Every workspace also comes with `.aiinbx.app`, where every address sends and receives with no DNS to set up ([domains](https://docs.aiinbx.com/guides/domains)). I wrote up [why the inbox is the wrong unit for a platform](/blog/why-inboxes-are-the-wrong-primitive) separately. - Customer subdomains need no DNS of their own. Verify a wildcard such as `*.saas.com` once, and each customer's subdomain is one API call ([wildcard domains](/features/wildcard-domains)). Receiving providers such as Gmail still judge mail by the domain it's signed with, so a customer who wants a reputation wholly their own connects their own domain. - Your users' Gmail and Outlook connect through your own OAuth app, with the same threads and events as your domains ([mailboxes](https://docs.aiinbx.com/guides/mailboxes)). - [Spaces](/features/spaces) hold each customer's domains, mailboxes, mail, pacing rules and suppression lists. Each space sends on a reputation of its own: bounces and complaints count against the space the mail left from, and a space over the line is paused by itself ([one reputation per space](https://docs.aiinbx.com/guides/spaces#one-reputation-per-space)). AgentMail can pause a single inbox or pod, but it [weighs](https://docs.agentmail.to/knowledge-base/account-suspended) bounce and complaint signals across your organisation's mail and can also suspend the whole account. - AI Inbx API keys act for the workspace: your customers call your API, and your backend calls ours. I wouldn't hand provider keys to customers, because it ties them to your email vendor and moves your auth boundary into someone else's system ([more on keys](/blog/ai-inbx-vs-agentmail#keys-for-your-customers)). An agent that holds its own credential with no backend in between signs in as an inbox through the [inbox MCP server](https://docs.aiinbx.com/guides/agent-inbox) or `aiinbx login --inbox`, and sees only the threads its address is on. ### Replies your code can act on - Threads hold without reply headers. On AI Inbx a reply joins its conversation when a client drops the headers, a colleague answers from another address or the subject changes, and a shared "Re: Invoice" alone never merges two conversations ([threading](https://docs.aiinbx.com/guides/receiving#threading)). Like a person reading the mail, AI Inbx recognises the conversation a reply continues before your code sees it; with header-only threading, a reply that lost its headers starts a new thread, and your agent has to search earlier mail for the conversation, at a cost in tokens and time. AgentMail [threads by](https://docs.agentmail.to/knowledge-base/threaded-conversations) `Message-ID`, `In-Reply-To` and `References` and doesn't describe replies without them, OpenMail [starts a new thread](https://docs.openmail.sh/concepts/threading) when no reply header matches, and Nuntly [falls back](https://nuntly.com/docs/guides/receiving-threads) to the same subject in the same inbox within seven days. - Answers inside the quote stay in place. AI Inbx's `stripped_text` drops the quoted conversation and a repeated signature, and keeps an answer typed into the quote under the line it answers, also when Outlook leaves the quote unmarked and the message answered is on the thread. `segments` gives the written, quoted and signature parts in order, and `stripped_html` makes the same cut for display ([what was written](https://docs.aiinbx.com/guides/receiving#what-was-written)). AgentMail keeps inline answers by leaving the whole message, quoted history included, in [`extracted_text`](https://docs.agentmail.to/reply-extraction), so your agent has to tell the new lines from the old ones itself. - Replies go where a mail client would send them. `threads.reply` derives the sender, recipients, subject and reply headers and follows a Reply-To. With `email_id` it answers the email your agent was handed, even when an out-of-office lands on the thread while it writes, and a Reply-To naming only your own addresses fails with `no_recipients` instead of mailing yourself ([replying](https://docs.aiinbx.com/guides/threads#replying)). - Automated mail is labelled and read. Every inbound email on AI Inbx has a `category`, such as `human`, `out_of_office`, `auto_reply` or `verification`, so an autoresponder isn't treated as an answer. An away reply carries `unavailable.back_on` and `unavailable.contacts`, so a sequence can wait for the return date or turn to the colleague named. A verification email carries `verification.code` and `verification.link`, so an agent can finish a sign-up ([automated mail](https://docs.aiinbx.com/guides/receiving#what-automated-mail-asks-for)). None of the other seven here documents a return date as a field. MailSlurp extracts codes through a separate request, and Nylas's CLI reads them. - Attachments arrive as text with the email. PDFs, documents and spreadsheets are prepared as Markdown or text while the message is taken in, so the text is normally there by the time `email.received` reaches you, and one `emails.retrieve` with `include: ["attachment_content"]` returns it with the message. Scanned PDF pages are read too, counted against a monthly page allowance ([attachments](https://docs.aiinbx.com/guides/attachments)). AgentMail [extracts PDF text](https://docs.agentmail.to/reply-extraction) from the text layer only, so a scanned PDF comes back without text. MailSlurp and Sendmux (now Qubrics) extract text on a separate request, and Sendmux reads no scanned pages. ### Outreach inside the rules AI Inbx allows outreach the recipient's law permits, and keeps it inside the limits you set: - [Pacing](/features/pacing) rules cap sends per sending address, sending domain, recipient or recipient domain over a rolling window. Mail over a cap waits in a queue you can see and release, rather than failing, so a burst goes out at the pace you set instead of all at once. AgentMail's docs give plan limits per day and per five minutes and a [warm-up schedule](https://docs.agentmail.to/email-deliverability) you follow yourself. Sendmux (now Qubrics) documents quotas on your own sending accounts, with mail over a cap held, and Nylas a daily quota per Agent Account that rejects sends over it. - [Sending hours](/features/sending-hours) hold mail outside the windows you set, such as weekdays 9:00 to 17:00 in `Europe/London` for recipients at `*.co.uk`, with daylight saving handled. None of the other seven documents a sending-hours setting. - [Suppressions](/features/suppressions) come from bounces of dead addresses, complaints, unsubscribe links, one-click unsubscribes and opt-out replies. A reply asking to stop arrives as `email.unsubscribed` with `source: "reply"`. None of the other seven documents opt-out replies being suppressed for you. - Open and click events carry `bot` and `bot_reason`, so Apple Mail Privacy Protection fetches and security scanners don't count as a person reading or trigger a follow-up. AgentMail's [open-tracking docs](https://docs.agentmail.to/knowledge-base/open-tracking) say proxy and scanner loads can register an open and advise treating very fast opens with suspicion. AI Inbx also has drafts for approval, scheduled sends, idempotent retries, two MCP servers and a CLI, so those move across; the [migration table](/blog/ai-inbx-vs-agentmail#moving-from-agentmail-to-ai-inbx) maps each call. ### Built for agents at volume I built AI Inbx for email agents at scale, and the reading above is what keeps the work per email small as volume grows: the agent reads only what a reply adds (I think `stripped_text` is the best reply stripping you can get from an email API), finds the conversation already matched, hands no automated mail to a model and parses no attachment twice. Pacing rules are checked on every send, up to 100 on Developer, 1,000 on Growth and no limit on Scale, and [spaces](https://docs.aiinbx.com/guides/spaces) keep each customer's rules apart under your workspace-wide limits. **What you'd give up:** AI Inbx has no free plan and no SOC 2 report. AI Inbx is an HTTP API with no IMAP or SMTP access and no templates or email builder, and it isn't self-hostable. Connected mailboxes are Gmail and Outlook only, through your own OAuth app, and SDKs are TypeScript and Python. **Pricing:** AI Inbx plans count emails, sent and received alike, never addresses. Developer is $5 a month for 5,000 emails, 50 domains and 100 connected mailboxes. Unlimited domains and mailboxes start at $29 a month (Growth, 30,000 emails); Scale is $99 for 100,000. Extra emails are $1 per 1,000 once you turn on extra usage ([pricing](/pricing)). ## Nylas (Agent Accounts) Nylas connects to your users' Google, Microsoft, Exchange, iCloud, Yahoo and IMAP accounts. Nylas's [Agent Accounts](https://developer.nylas.com/docs/changelogs/2026-06-17-agent-accounts-ga/), generally available since June 2026, are Nylas-hosted mailboxes on your domain. **Better than AgentMail:** - Nylas reaches users' existing mailboxes, including Exchange on-premises over EWS and [IMAP](https://developer.nylas.com/docs/provider-guides/imap/). - Nylas has SDKs for Node.js, Python, Ruby and Kotlin/Java, and a [Templates API](https://developer.nylas.com/docs/v3/email/templates-workflows/). - Nylas's meter is smaller: $0.40 a month per extra Agent Account on Pro ($0.20 on annual billing) against AgentMail's $2, so the 500-address bill comes to $229 against $900. It still grows with every address. **What you'd give up:** Nylas's [reply guide](https://developer.nylas.com/docs/cookbook/email/threads/reply-to-a-thread/) has the caller set recipients and subject, Nylas [states](https://developer.nylas.com/docs/cookbook/email/sendgrid-alternative/) it doesn't ship suppression lists, and attachments come without extracted text. Each customer subdomain is registered as its own domain and counts against 1, 10 or 20 custom sending domains. On outreach, Nylas's [Terms](https://www.nylas.com/legal/terms/) bar unsolicited email while the Agent Accounts docs list a sales agent that "runs cold outreach campaigns"; ask Nylas before you rely on either. **Pricing:** Nylas Essentials is $15 a month with 10 connected accounts (+$2.25 each) and 10 Agent Accounts. Pro is $49 ($43 annual) with 25 connected accounts (+$2.00), 50 Agent Accounts (+$0.40) and 50,000 Agent Account emails ([pricing](https://www.nylas.com/pricing/)). Agent Accounts count cumulatively, so one deleted mid-month still counts. 1,000 connected users on Pro come to $1,999 a month. **Pick Nylas if** your product works inside users' existing mailboxes, especially Exchange or IMAP. ## Resend (Inboxes) Resend is an email API with sending, receiving, templates, Broadcasts and Automations. Resend's [Inboxes](https://resend.com/blog/announcing-inboxes), announced on 22 October 2026, group sent and received mail into threads. **Better than AgentMail:** - Resend [receives mail for any address](https://resend.com/docs/dashboard/receiving/introduction) at a domain once the MX record is added. Threads need an inbox. - Resend's meter is smaller: $1 a month per extra inbox against AgentMail's $2, and Pro includes 50,000 emails for $20, sent and received counted together. It still grows with every inbox. - Resend has hosted templates with a no-code editor, React Email, Broadcasts, nine official [SDKs](https://resend.com/docs/sdks) and a SOC 2 Type II report. **What you'd give up:** Resend's [received-email object](https://resend.com/docs/api-reference/emails/retrieve-received-email) carries the full bodies with no field for the newly written text, and attachments come as a download URL valid for an hour, without extracted text. Resend's [multi-tenant guide](https://resend.com/docs/knowledge-base/setting-up-resend-for-multi-tenants) uses domain-scoped API keys and tags, or a team per customer that can't be created through the API, and says tenants in one account share its sender reputation. Each subdomain is verified with its own DNS records and counts toward the domain limit (10 on Pro, 1,000 on Scale). Resend's [Acceptable Use Policy](https://resend.com/legal/acceptable-use) prohibits cold outreach. **Pricing:** Resend Pro is $20 for 50,000 emails and $35 for 100,000; Scale starts at $90. Overage is $0.90 per 1,000, and every email through an inbox counts ([pricing](https://resend.com/pricing)). **Pick Resend if** sending is most of your email and you need a few threaded inboxes beside it, with templates and Broadcasts in the same account. ## OpenMail OpenMail gives each agent its own inbox through an API, CLI or MCP server. OpenMail's product shape is the closest to AgentMail's in this list. **Better than AgentMail:** - OpenMail's [terms](https://openmail.sh/terms) allow individual, relevant B2B outreach without prior opt-in where lawful: from your own verified domain, to business addresses you didn't buy, with an opt-out and at most two follow-ups, under a daily cap on new recipients. - OpenMail gives each inbound message a [category](https://docs.openmail.sh/pages/webhooks/events) and an `auto_replyable` flag, and its [attachment text](https://docs.openmail.sh/concepts/attachments) covers images through OCR. - OpenMail's meter is smaller: €1 a month per extra inbox against AgentMail's $2, with unlimited pods on every plan and no seat fees. It still grows with every inbox. **What you'd give up:** OpenMail's [send endpoint](https://docs.openmail.sh/api-reference/messages/send-email) has no scheduling, and the API reference lists no drafts. OpenMail documents quote stripping for its MCP `read_thread` tool, not for the API body fields. OpenMail's pages don't document a Python SDK, open tracking, IMAP and SMTP or a SOC 2 report. OpenMail has no catch-all either: mail for an address with no inbox is dropped. **Pricing:** OpenMail Pro is €9 a month with 10 inboxes, 10,000 emails and 10 GB, then €1 per inbox, €0.001 per email and €0.10 per GB ([pricing](https://openmail.sh/pricing)). OpenMail's [docs](https://docs.openmail.sh/concepts/rate-limits) list 10 sends a minute and 200 a day per inbox, while the pricing page lists no daily cap on Pro. **Pick OpenMail if** you want AgentMail's inbox-per-agent model with room for lawful B2B outreach. ## MailSlurp MailSlurp provides email addresses, connected mailboxes and phone numbers through an API, with tools for testing email and SMS flows. **Better than AgentMail:** - MailSlurp gives each custom domain a [catch-all inbox](https://www.mailslurp.com/docs/custom-domains/). - MailSlurp's [connectors](https://www.mailslurp.com/docs/connectors/) sync Gmail, Google Workspace, Outlook and Microsoft 365 mailboxes over IMAP and SMTP. - MailSlurp has SDKs from TypeScript and Python to Swift and Dart, endpoints that wait for an email, SMS numbers and inbox placement tests. **What you'd give up:** sending. MailSlurp's [pricing](https://app.mailslurp.com/pricing/) page lists sending to external addresses from Pro, with 500 a month included on Pro and Growth, and the docs require double opt-in consent or a support whitelist for external recipients. MailSlurp lists isolated environments under Enterprise, and its trust centre lists SOC 2 Type 1. **Pricing:** MailSlurp plans grow with emails received and inboxes created. Pro is $69 a month for commercial use: 5,000 emails received, 1,000 inboxes created a month and 500 external sends. Growth is $199 with 5,000 inboxes a month and one custom domain. **Pick MailSlurp if** you test signup, OTP and password-reset flows in CI, or need many short-lived addresses that mostly receive. ## Nuntly Nuntly sends and receives transactional email, with open and click tracking and webhooks. **Better than AgentMail:** - Nuntly creates a [catch-all inbox](https://nuntly.com/docs/guides/receiving-inboxes) (`*`) when you enable receiving, for every address without an inbox of its own. - Nuntly prices by volume: Starter is €16 for 50,000 emails and €28 for 100,000, and Scale runs from €68 for 100,000 to €625 for 1,500,000. - Nuntly has open and click tracking with an optional `isBotEvent` field, and versioned templates and Broadcasts. **What you'd give up:** Nuntly doesn't document reply text without the quote or attachment text. Nuntly's suppression list is reviewed through support, and drafts exist for Broadcasts only. Nuntly's [namespaces](https://nuntly.com/docs/guides/receiving-namespaces) group inboxes per tenant, but domains, webhooks and API keys carry no namespace. Official SDKs are TypeScript and Java, and the docs list cold outreach as not allowed. **Pricing:** Nuntly's named inboxes step up with the plan, from 1 on Free to 10 on Starter, 100 on Scale and unlimited on Enterprise ([pricing](https://nuntly.com/pricing)). With the catch-all inbox doing the receiving, the email tier matters more than the inbox cap. **Pick Nuntly if** you need transactional sending with inbound threads and catch-all receiving, priced by volume. ## Sendmux (now Qubrics) Sendmux, renamed Qubrics in its app and API in November 2026, routes outbound mail through your own Gmail, Outlook and SMTP accounts or its managed sending, with agent mailboxes and usage-based billing. **Better than AgentMail:** - Sendmux connects users' [Gmail and Outlook accounts](https://sendmux.ai/docs/sending/accounts/google-microsoft) as sending accounts with send-only scopes, alongside custom SMTP accounts. - Sendmux takes per-hour and per-day caps on each of your sending accounts (custom SMTP accounts per-second and per-minute [quotas](https://sendmux.ai/docs/sending/accounts) too), and holds mail over a cap. - Sendmux documents [cold outreach](https://sendmux.ai/docs/use-cases/cold-email-outreach) through your own accounts as a use case, charges no per-mailbox fees and has SDKs for TypeScript, Python, Go, PHP, Ruby and Rust. **What you'd give up:** a Sendmux team is the isolation boundary, so each isolated customer is its own Pro team at $7 a month. Sendmux doesn't document a suppression list or open tracking, and its [enterprise page](https://sendmux.ai/solutions/enterprise/) says it is not certified against a specific standard yet. Catch-all is listed as planned. **Pricing:** Sendmux charges $0.50 per 1,000 recipients through your own providers, $0.75 per 1,000 through managed sending, $0.50 per 1,000 inbound deliveries and $0.02 per GB-month, with every To, CC and BCC recipient counted ([pricing](https://sendmux.ai/pricing/)). **Pick Sendmux if** your product sends from users' own Gmail, Outlook or SMTP accounts and needs caps and failover across them. ## What 500 addresses and 50,000 emails a month cost For a platform, the address count decides most of the bill. AI Inbx has no meter on addresses, inboxes or accounts; five of the other seven charge per inbox or connected account, and Sendmux per isolated customer team. I don't pitch AI Inbx as the cheap option. I think our pricing is fair: it follows what email costs to send, receive and store, and at these prices AI Inbx runs as a healthy business. An extra inbox costs a provider close to nothing, so in my view a monthly fee per inbox is margin, not cost. Take a platform with 500 agent addresses on up to 10 of its own domains that sends 30,000 emails and receives 20,000 a month, one recipient each, at list prices on monthly billing, November 2026: ``` AgentMail Startup ($200, 150 inboxes) $200.00 350 extra inboxes x $2 $700.00 Total $900.00 Resend Pro ($20, 50,000 emails, 3 inboxes) $20.00 497 extra inboxes x $1 $497.00 Total $517.00 OpenMail Pro (€9, 10 inboxes, 10,000 emails) €9.00 490 extra inboxes x €1 €490.00 20,000 to 40,000 extra emails x €0.001 €20.00 to €40.00 Total €519.00 to €539.00 Nylas Pro ($49, 50 Agent Accounts) $49.00 450 extra Agent Accounts x $0.40 $180.00 Total $229.00 AI Inbx Growth ($29, 30,000 sent or received) $29.00 20,000 extra emails x $0.001 $20.00 Total $49.00 Sendmux Pro (one team) $7.00 30,000 managed sends x $0.00075 $22.50 20,000 inbound deliveries x $0.0005 $10.00 Total $39.50 plus storage ``` Notes on the rows: - AgentMail Developer would cost more, because past the plan it charges twice, per extra inbox and per 1,000 extra sends: $1,040 ($20, 490 extra inboxes and 20 blocks of 1,000 extra sends at $2 each). AgentMail's plan limits are [sending limits](https://docs.agentmail.to/knowledge-base/rate-limits), and Startup allows 15,000 a day. - Resend counts every email sent or received through an inbox, so the 50,000 here use Pro's whole allowance. Resend Pro and Nylas Pro each include 10 domains, hence the domain count. - OpenMail's pricing page says "emails" without saying whether received mail counts, hence the range. - Nylas's 50,000 emails are Agent Account sends; storage and bandwidth past 50 GB each are extra. - AI Inbx bills extra emails only once extra usage is turned on; without it, sending stops at 30,000 while receiving continues. - Sendmux costs less than AI Inbx here. Sendmux Pro lists mailboxes as unlimited under fair usage and starts managed sending at 1,000 recipients a day, which 30,000 a month averages out to. If every address belongs to a customer you must isolate, Sendmux needs a $7 team per customer, while AI Inbx spaces and AgentMail Pods are included. - Nuntly costs less than every row above: Starter at €16 covers 50,000 emails even if received mail counts, with the catch-all inbox receiving for all 500 addresses. 500 named inboxes would need Enterprise. - MailSlurp's Pro and Growth plans include 500 external sends and 5,000 received emails a month. Growth bills extra sends and received emails at usage rates its pricing page doesn't list, so this bill can't be worked out from published prices. At 5,000 addresses, with the same 50,000 emails on up to 10 domains, AgentMail Startup comes to $9,900 ($200 plus 4,850 extra inboxes at $2; Enterprise is priced on request). Resend Pro comes to $5,017 ($20 plus 4,997 inboxes at $1), OpenMail Pro to €5,019 to €5,039 (€9 plus 4,990 inboxes at €1, plus €20 to €40 of emails) and Nylas Pro to $2,029 ($49 plus 4,950 Agent Accounts at $0.40). AI Inbx Growth stays at $49, Sendmux at $39.50 on one team and Nuntly at €16. ## Which AgentMail alternative should you choose? - **Addresses on your domains for customers or agents:** AI Inbx. - **Acting on replies and automated mail:** AI Inbx. - **Users' own Gmail and Outlook:** AI Inbx; Nylas for Exchange and IMAP too; Sendmux (now Qubrics) to send through them only. - **Cold outreach tools:** AI Inbx; Sendmux for sending through users' own accounts; OpenMail for individual B2B outreach under its terms. See also [email APIs for cold outreach tools](/blog/email-api-for-cold-outreach-tools). - **One personal agent holding its own credential:** AI Inbx's inbox scope (`aiinbx login --inbox`); OpenMail, Resend or Nylas Agent Accounts if you want an inbox object per agent. - **Sending first, with templates and Broadcasts:** Resend. - **The lowest list price at volume:** Nuntly, then Sendmux. - **Email tests in CI:** MailSlurp. ## When to stay on AgentMail Stay if one inbox per agent is the shape of your product and the inbox count stays modest. AgentMail is the better fit when: - Each agent needs an IMAP and SMTP login of its own. - You need a free plan and a SOC 2 Type II report from the same vendor. - You need Enterprise options: Outposts in your own AWS account, dedicated IPs or SSO. - You use WebSockets for real-time mail. - Your mail goes to people who asked for it, and your users don't need their own mailboxes connected. Platforms that hand AgentMail addresses to their own customers should read [Terms](https://www.agentmail.to/legal/terms) §4(c), which grants integration into "your own platform or application" "subject to your subscription tier", and ask AgentMail which tier that means. Its [multi-tenancy guide](https://docs.agentmail.to/multi-tenancy) says to give each customer a pod-scoped API key, while the same Terms (§8(l)) forbid making "your API keys or account credentials" available to any third party. For a side-by-side on every row, read [AI Inbx vs AgentMail](/blog/ai-inbx-vs-agentmail); for the wider field, [email APIs for AI agents](/blog/best-email-api-for-ai-agents). To try ours, start with the [quickstart](https://docs.aiinbx.com) or compare [plans](/pricing). *Last checked: 6 November 2026. Work at one of these companies and spotted something wrong? Email [pau@aiinbx.com](mailto:pau@aiinbx.com) with a link and I'll correct it.* Written by [Pau Kraft](https://paukraft.com) [@paukraft on X](https://x.com/paukraft) Before AI Inbx, Pau built email agents that run in production for enterprises in the sourcing industry, processing thousands of emails a month, where a single reply filed on the wrong conversation is not acceptable. AI Inbx is built on what those systems taught him: the threading edge cases, the replies cut in the wrong place, the email that went out at 02:30 on a Sunday. ## Questions ### What is the best alternative to AgentMail? For a product that gives its own customers or agents email, I think AI Inbx: every address on your domains works without being created, the bill follows email volume, and replies, out-of-office mail and opt-outs arrive already read. For users' Exchange or IMAP accounts, Nylas. For transactional sending with a few inboxes, Resend. For AgentMail's inbox-per-agent model with lawful B2B outreach, OpenMail. For email tests in CI, MailSlurp. ### Does AgentMail support catch-all email addresses? No. AgentMail's blog states that it does not offer catch-all, so each address needs an inbox before it receives. AI Inbx, Resend, Nuntly and MailSlurp accept mail for any address on a domain once receiving is set up. ### Can AgentMail connect to a user's Gmail or Outlook account? No. AgentMail's docs describe no way to read or send from an existing Gmail or Outlook mailbox. AI Inbx connects both through your own OAuth app, in the same API as your domains. Nylas also connects Exchange and IMAP accounts, MailSlurp syncs mailboxes over IMAP and SMTP, and Sendmux (now Qubrics) sends through them without reading them. ### Can I use AgentMail for cold email? No. AgentMail's docs say it does not support cold outreach, and its Terms (§8(h)) prohibit unsolicited email. Resend and Nuntly prohibit it too. AI Inbx, OpenMail and Sendmux (now Qubrics) allow outreach within the law, each with its own conditions, so read their terms before you send. ### Does AgentMail handle unsubscribe replies automatically? No. AgentMail's cold-outreach page tells you to read a reply's extracted\_text, decide whether it is an opt-out and block the address yourself. AI Inbx suppresses the address and sends email.unsubscribed with source reply. None of the other alternatives here documents that. ### How much does AgentMail cost per inbox? As of November 2026, Free includes 3 inboxes, Developer ($20 a month) 10 and Startup ($200 a month) 150. On Developer and Startup each extra inbox is $2 a month, or $19.20 a year on yearly plans. Enterprise is custom, with up to unlimited inboxes and usage-based pricing. ### Is AgentMail free? AgentMail has a free plan with no credit card: 3 inboxes, 3,000 emails a month (100 a day), 3 GB of storage and 2 seats, with a 'Sent via AgentMail' footer on outgoing mail. The pricing page lists 1 custom domain on Free, while AgentMail's docs say custom domains start on Developer. ### Which AgentMail alternative costs less at scale? For 500 addresses, 30,000 emails sent and 20,000 received a month, list prices come to $900 on AgentMail Startup, $517 on Resend Pro, €519 to €539 on OpenMail Pro, $229 on Nylas Pro, $49 on AI Inbx Growth, $39.50 on one Sendmux Pro team and €16 on Nuntly Starter. Sendmux and Nuntly cost less, but neither documents opt-out replies or sending hours, and Sendmux needs a $7 team for each customer you isolate. ### Does AI Inbx replace AgentMail? Yes, if your product gives customers or agents addresses on your domains, works in your users' Gmail or Outlook, acts on replies, or sends paced outreach. No, if you need a free plan, a SOC 2 report, IMAP or SMTP access, or a deployment in your own cloud account. Keep reading ## More from the blog [All posts](/blog) - [5 November 2026ComparisonsAI Inbx vs AgentMail: inboxes vs addresses (2026)AgentMail bills per inbox; on AI Inbx every address works and the bill follows email. Threads, out-of-office dates, opt-outs, pacing and three worked bills.Pau Kraft](/blog/ai-inbx-vs-agentmail) - [5 November 2026ComparisonsBest email APIs for AI agents (2026)Why I think AI Inbx is the best email API for products that give agents email, the bugs it saves you from, and when AgentMail, Nylas or Postmark fit better.Pau Kraft](/blog/best-email-api-for-ai-agents) - [5 November 2026ComparisonsBest email APIs for cold outreach tools (2026)What a cold-outreach product needs from its email API, and how 12 providers compare on terms, send limits, sending hours, replies and per-customer separation.Pau Kraft](/blog/email-api-for-cold-outreach-tools) - [5 November 2026ComparisonsThe best Nylas alternatives (2026)Aurinko, Unipile, EmailEngine and AI Inbx vs Nylas for Gmail and Outlook products: threading, reply text, out-of-office dates, opt-outs, cost per account.Pau Kraft](/blog/nylas-alternatives) ## Give your product an inbox. The hard parts are already handled. 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