Best email APIs for AI agents in 2026
For an AI agent that sends email to your users, Unitpost ranks first: a hosted MCP server with browser sign-in, scoped keys, and a sending gate that checks domains, suppressions and consent on every call. AgentMail is the better pick when the agent needs inboxes of its own. Resend, MailerSend, Mailgun and Postmark all publish official MCP servers too.
Updated November 2, 2026. We make Unitpost, and it is on this list. Every score has a reason and the weights are published below, so you can re-rank it for your own needs. How we scored
| # | Product | Best for | Score |
|---|---|---|---|
| 1 | Unitpost | agents that send to your users | 4.8 |
| 2 | AgentMail | agents that need their own inboxes | 4.3 |
| 3 | Resend | developers already on Resend | 3.8 |
| 4 | MailerSend | a hosted MCP on a small budget | 3.5 |
| 5 | Mailgun | agents on a high-volume API | 3.2 |
| 6 | Postmark | agents sending critical mail | 3.2 |
The picks
#1 · 4.8 / 5
Unitpost
Best for agents that send to your usersA hosted MCP server with one tool per API operation, behind the same scopes, sending gate and quota as the REST API. Unit, the dashboard assistant, asks before anything sends.
Pros
- Hosted MCP server with OAuth sign-in, or a key for headless clients
- Every call passes the sending gate: domain, suppressions and consent
- Docs as Markdown, llms.txt and an agent skill
- 5,000 emails a month free
Cons
- Inbound arrives on your domain, not in per-agent inboxes
- SMS tools need a paid plan
- Free plan
- 5,000 emails a month, 200 a day, no card
- Paid from
- $10 a month for 20,000 emails
- Priced by
- Emails sent
#2 · 4.3 / 5
AgentMail
Best for agents that need their own inboxesAn API that gives each agent an email inbox to send from, receive into and search, with IMAP and SMTP as well as REST. Built for the agent's own mail more than for mailing your customers.
Pros
- Inboxes for agents are the core product
- Official hosted MCP server
- REST, SMTP and IMAP access
Cons
- No custom domains on the free plan, and a footer on free mail
- No marketing email or audience tools
- Free plan
- 3 inboxes, 3,000 emails a month, 100 a day
- Paid from
- $20 a month for 10 inboxes
- Priced by
- Inboxes and sends
#3 · 3.8 / 5
Resend
Best for developers already on ResendA modern email API with an official MCP server, local or hosted, and inbound email on every plan.
Pros
- Official MCP server, local or hosted
- Inbound email on every plan
- Sending-only API keys
Cons
- Nothing holds an agent's send for approval
- Free sending is capped at 100 a day
- Free plan
- 3,000 emails a month, 100 a day
- Paid from
- $20 a month for 50,000 emails
- Priced by
- Sends and contacts
#4 · 3.5 / 5
MailerSend
Best for a hosted MCP on a small budgetA transactional email API with an official hosted MCP server and a $7 first paid plan. The free plan is small.
Pros
- Official hosted MCP server
- Inbound routing
- Hobby is $7 a month for 5,000 emails
Cons
- 500 emails a month on free
- Inbound mail counts against the monthly quota
- Free plan
- 500 emails a month, card required
- Paid from
- $7 a month for 5,000 emails
- Priced by
- Emails sent
#5 · 3.2 / 5
Mailgun
Best for agents on a high-volume APIA long-running email API with an official MCP server you run yourself, and inbound routes that parse incoming mail.
Pros
- Official MCP server
- Inbound routes parse incoming mail
- Proven at very high volume
Cons
- The MCP server runs locally only
- One inbound route and one day of logs on free
- Free plan
- 100 emails a day on one domain
- Paid from
- $15 a month for 10,000 emails
- Priced by
- Emails sent
#6 · 3.2 / 5
Postmark
Best for agents sending critical mailTransactional email with a strong deliverability record and an official MCP server from ActiveCampaign that runs locally.
Pros
- Official MCP server
- The best-regarded deliverability record here
- Inbound on most plans
Cons
- The MCP server runs locally only
- 100 emails a month on free
- Free plan
- 100 emails a month
- Paid from
- $15 a month for 10,000 emails
- Priced by
- Emails sent
Scores side by side
| Product | MCP server25% | Send safety25% | Reading replies20% | Agent-readable docs15% | Free plan15% | Total |
|---|---|---|---|---|---|---|
| Unitpost | 5 | 5 | 4 | 5 | 5 | 4.8 |
| AgentMail | 5 | 4 | 5 | 4 | 3 | 4.3 |
| Resend | 4 | 3 | 4 | 4 | 4 | 3.8 |
| MailerSend | 5 | 3 | 3 | 4 | 2 | 3.5 |
| Mailgun | 3 | 3 | 4 | 3 | 3 | 3.2 |
| Postmark | 3 | 3 | 4 | 4 | 2 | 3.2 |
How we scored
This list is for developers giving an AI agent (Claude, Cursor, Codex or their own) the ability to send email on a product's behalf. What matters: an official MCP server, controls that stop an agent from mailing the wrong people, a way to read replies, docs an agent can follow, and a free way to try it.
- MCP server (25%). An official MCP server, hosted, with sign-in in the browser rather than a pasted key.
- Send safety (25%). Scoped keys, idempotent sends, and checks an agent can't skip before anything sends.
- Reading replies (20%). The agent can receive and read mail, on your domain or its own inbox.
- Agent-readable docs (15%). Docs as Markdown or llms.txt, structured errors, and an agent skill.
- Free plan (15%). A permanent free plan large enough to run a small app on, with no card.
Each product gets 1 to 5 per criterion, from its own pricing and docs pages. The total is the weighted mean, so changing a weight re-ranks the list.
Why Unitpost scored 4.8
- MCP server: 5/5. Hosted, OAuth in the browser, one tool per API operation, keys as a fallback.
- Send safety: 5/5. Scoped keys, idempotency keys, and the sending gate on every MCP call; Unit asks before sending.
- Reading replies: 4/5. Inbound email on your domain, with a signed webhook per message and a shared inbox.
- Agent-readable docs: 5/5. Every docs page as Markdown, an llms.txt index and an installable agent skill.
- Free plan: 5/5. 5,000 emails a month free for good, 200 a day, no card.
Checked November 2, 2026 against unitpost.com/pricing, unitpost.com/sms, registry.npmjs.org/unitpost.
Why AgentMail scored 4.3
- MCP server: 5/5. An official hosted MCP server.
- Send safety: 4/5. Idempotency keys on sends, per-key permissions and inbound prompt-injection scanning; nothing holds a send for approval.
- Reading replies: 5/5. Receiving and reading mail in per-agent inboxes is what it is for.
- Agent-readable docs: 4/5. Clear REST docs with SMTP and IMAP guides.
- Free plan: 3/5. 3 inboxes and 3,000 emails a month, without custom domains.
Checked November 2, 2026 against agentmail.to/pricing, docs.agentmail.to/integrations/mcp, docs.agentmail.to/imap-smtp, docs.agentmail.to/idempotency.md, docs.agentmail.to/llms.txt, docs.agentmail.to/overview.
Why Resend scored 3.8
- MCP server: 4/5. An official server, run locally or hosted at mcp.resend.com.
- Send safety: 3/5. Sending-only keys and idempotency keys; no approval step.
- Reading replies: 4/5. Inbound email on every plan, free included.
- Agent-readable docs: 4/5. A clear API with good docs and many SDKs.
- Free plan: 4/5. 3,000 emails a month free, capped at 100 a day.
Checked November 2, 2026 against resend.com/pricing, resend.com/migrate, resend.com/docs/dashboard/receiving/introduction, github.com/resend/mcp-send-email, resend.com/docs/send-with-smtp, resend.com/docs/api-reference/api-keys/create-api-key, registry.npmjs.org/resend, resend.com/docs/dashboard/webhooks/retries-and-replays.
Why MailerSend scored 3.5
- MCP server: 5/5. An official hosted MCP server with OAuth on every plan, covering email, SMS, domains and templates.
- Send safety: 3/5. API tokens and a sending API; nothing holds an agent's send for approval.
- Reading replies: 3/5. Inbound routing, counted against the monthly email quota.
- Agent-readable docs: 4/5. A modern REST API with clear docs.
- Free plan: 2/5. 500 emails a month on one domain.
Checked November 2, 2026 against mailersend.com/pricing, developers.mailersend.com/mcp, mailersend.com/help/smtp-relay, mailersend.com/features/inbound-emails, developers.mailersend.com/api/v1/webhooks.html, registry.npmjs.org/mailersend, developers.mailersend.com/api/v1/inbound.
Why Mailgun scored 3.2
- MCP server: 3/5. An official server, run locally; no hosted version.
- Send safety: 3/5. Domain-level sending keys; nothing holds an agent's send for approval.
- Reading replies: 4/5. Inbound routes forward and parse mail; one route on free.
- Agent-readable docs: 3/5. Thorough docs on a long-lived API surface.
- Free plan: 3/5. A free plan of 100 emails a day on one domain, with one day of logs.
Checked November 2, 2026 against mailgun.com/pricing/, mailgun.com/resources/guides/migrating-from-sendgrid-to-mailgun-email-api/, documentation.mailgun.com/docs/mailgun/mcp, documentation.mailgun.com/docs/mailgun/user-manual/sending-messages/send-smtp, registry.npmjs.org/mailgun.js, documentation.mailgun.com/docs/mailgun/user-manual/receive-forward-store/receive-http.
Why Postmark scored 3.2
- MCP server: 3/5. An official server from ActiveCampaign, run locally.
- Send safety: 3/5. Server tokens per server; no approval step for agents.
- Reading replies: 4/5. Inbound on Free, Pro and Platform, though not on Basic.
- Agent-readable docs: 4/5. A mature, well-documented API.
- Free plan: 2/5. 100 emails a month free, enough to test, not to run an app.
Checked November 2, 2026 against postmarkapp.com/pricing, postmarkapp.com/migration-guides, postmarkapp.com/lp/mcp, postmarkapp.com/developer/user-guide/send-email-with-smtp, registry.npmjs.org/postmark, postmarkapp.com/developer/webhooks/inbound-webhook.
Frequently asked questions
What is an MCP server for email?
How do I stop an agent from emailing the wrong people?
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Go deeper: Unitpost MCP server · Agent docs · Let an AI agent send email safely · What is an email MCP server? · Protect an agent from prompt injection
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