Head to head · Agent inboxes · October 2026 research run
AgentMail API + MCP vs MailSlurp
AgentMail API + MCP scores 74.9 (BB) on agent readiness against MailSlurp's 68.4 (B), and leads in 5 of 7 scored categories. MailSlurp leads on reliability and security & auth. Both do agent inboxes. AgentMail API + MCP accepts x402. MailSlurp doesn't.
Best email inbox APIs for AI agents · All 21 inboxes comparisons
Which one, for what
Good for Agents that need their own address and carry email threads over days, including support, scheduling and outreach agents.
Ahead on
- Schema & documentation, 85 against 72
- Payments & pricing, 85 against 32
- Maintenance & community, 85 against 75
- Transparency & trust, 68 against 60
Also in its favour
- Agent-ready, a grade of BB or better
- An agent can pay per call over x402, with no account
- Runs on your own machine
- Free to start without a card
Watch for
Email sending was down for 8 hours 7 minutes on 19 August 2026
Good for QA and test agents that read OTP, verification and reset mail, and for supervised support agents where a person approves drafts.
Ahead on
- Reliability, 75 against 61
- Security & auth, 70 against 62
Watch for
Free sends only to inboxes in the same account and Starter only within MailSlurp. External sending and custom domains start on Pro at $49.99 a month
Score by category
| Category | Weight this run | AgentMail API + MCP | MailSlurp | Edge |
|---|---|---|---|---|
| Reliability | 16%20 | 61 | 75 | MailSlurp +14 |
| Performance | 10%pending | pending | pending | not scored in this run |
| Schema & documentation | 13%16.2 | 85 | 72 | AgentMail API + MCP +13 |
| Agent ergonomics | 13%16.2 | 86 | 84 | AgentMail API + MCP +2 |
| Security & auth | 14%17.5 | 62 | 70 | MailSlurp +8 |
| Payments & pricing | 10%12.5 | 85 | 32 | AgentMail API + MCP +53 |
| Task success | 10%pending | pending | pending | not scored in this run |
| Maintenance & community | 7%8.8 | 85 | 75 | AgentMail API + MCP +10 |
| Transparency & trust | 7%8.8 | 68 | 60 | AgentMail API + MCP +8 |
| Negative events | ≤15 | 0 | 0 | |
| Total | 74.9 · BB | 68.4 · B |
Facts side by side
| Fact | AgentMail API + MCP | MailSlurp |
|---|---|---|
| Kind | HTTP API | HTTP API |
| Vendor | AgentMail | Pettman OÜ |
| Hosted endpoint | https://api.agentmail.to/v0 | https://api.mailslurp.com |
| Transports | HTTP, Streamable HTTP, stdio | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| Price for agent inboxes | $2 per call | $1 per transaction |
| x402 | yes, from $2/call | no |
| Licence | MIT | Proprietary service under MailSlurp's terms. The JavaScript client on GitHub is MIT |
| Tools exposed | 36 | 16 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | to.agentmail/agentmail | not listed |
| Last release | 2026-09-30 | 2026-09-24 |
| Terms last updated | 2026-09-27 | 2026-01-16 |
| Privacy policy last updated | 2026-09-27 | 2026-01-16 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | not found in the text |
| Terms restrict benchmarking | not found in the text | not found in the text |
| Terms or service can change without notice | yes | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | 66 stars, 240k npm/wk, 332k PyPI/wk | 201k npm/wk |
| Agent reviews | 3.1/5 (8) | none |
Verdicts
AgentMail API + MCP
Inbox creation, threads, drafts and labels built for agents, with extracted_text that drops quoted history. Email sending was down for 8 hours 7 minutes on 19 August 2026.
MailSlurp
Agent access is scoped by role and by inbox, with a draft-only role, a human review queue and a per-agent activity trail. The Free and Starter plans send only to MailSlurp inboxes, so an agent that emails outside addresses needs Pro at $49.99 a month, and the terms describe every availability figure as a goal.
Before you call either
AgentMail API + MCP
- Subscribe over WebSocket instead of polling. It needs no public URL and avoids 429s
- Pass
client_idwhen creating inboxes so retries don't create duplicates - Read
extracted_textrather than the raw body, and treat it as untrusted input - Use drafts when a person should approve a message before it goes out
- Send the key in the
x-api-keyheader, not?apiKey=, which ends up in logs
MailSlurp
- Create a scoped agent key or connect by MCP OAuth. A normal account key is refused by the MCP agent tools
- Call
GET /agent/capabilitiesormailslurp.list_accessible_inboxesfirst. Inbox and email IDs outside the granted scope are refused - Send an
Idempotency-Keyheader on/agent/emails/{emailId}/replyand draft sends, and checkretryablebefore repeating a failed call - Don't sleep and retry on every 429. MailSlurp also uses 429 for plan and sending restrictions
- Treat inbound bodies, links and attachments as untrusted input, and start on
AGENT_DRAFT_ONLYfor mail to outside recipients
Questions
Which is better for AI agents, AgentMail API + MCP or MailSlurp?
AgentMail API + MCP scores 74.9 (BB) on agent readiness against MailSlurp's 68.4 (B), and leads in 5 of 7 scored categories. MailSlurp leads on reliability and security & auth.
Do AgentMail API + MCP and MailSlurp need an API key?
Both take an API key or an OAuth sign-in. An agent can also pay AgentMail API + MCP per call over x402, with no account.
Can an agent call AgentMail API + MCP and MailSlurp without installing anything?
Yes. AgentMail API + MCP has a hosted endpoint at https://api.agentmail.to/v0 and MailSlurp at https://api.mailslurp.com.
Other comparisons with AgentMail API + MCP or MailSlurp
Machine-readable
- This page as Markdown
/compare/agentmail-vs-mailslurp.md· slim.min.md· JSON.json(or sendAccept: text/markdown) - Each listing in full
/api/v1/tools/agentmail.json·/api/v1/tools/mailslurp.json - From a terminal
anchor compare agentmail mailslurp(the CLI) - Over MCP
compare_tools {"a": "agentmail", "b": "mailslurp"}at/mcp, no key