Head to head · Agent inboxes · October 2026 research run
AgentMail API + MCP vs InboxAPI
AgentMail API + MCP scores 74.9 (BB) on agent readiness against InboxAPI's 54.5 (C), and leads in every scored category. Both do agent inboxes. AgentMail API + MCP accepts x402. InboxAPI 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
- Reliability, 61 against 33
- Schema & documentation, 85 against 69
- Agent ergonomics, 86 against 61
- Security & auth, 62 against 57
- Payments & pricing, 85 against 53
- Maintenance & community, 85 against 63
- Transparency & trust, 68 against 53
Also in its favour
- Agent-ready, a grade of BB or better
- An agent can pay per call over x402, with no account
Watch for
Email sending was down for 8 hours 7 minutes on 19 August 2026
InboxAPI C
Good for A personal mailbox for one coding agent that needs to exchange mail with its owner and a few contacts at no cost.
Also in its favour
- No key needed to call it
Watch for
Mail arrives by polling only. No webhook, websocket or push tool was found in the tool list or docs
Score by category
| Category | Weight this run | AgentMail API + MCP | InboxAPI | Edge |
|---|---|---|---|---|
| Reliability | 16%20 | 61 | 33 | AgentMail API + MCP +28 |
| Performance | 10%pending | pending | pending | not scored in this run |
| Schema & documentation | 13%16.2 | 85 | 69 | AgentMail API + MCP +16 |
| Agent ergonomics | 13%16.2 | 86 | 61 | AgentMail API + MCP +25 |
| Security & auth | 14%17.5 | 62 | 57 | AgentMail API + MCP +5 |
| Payments & pricing | 10%12.5 | 85 | 53 | AgentMail API + MCP +32 |
| Task success | 10%pending | pending | pending | not scored in this run |
| Maintenance & community | 7%8.8 | 85 | 63 | AgentMail API + MCP +22 |
| Transparency & trust | 7%8.8 | 68 | 53 | AgentMail API + MCP +15 |
| Negative events | ≤15 | 0 | 0 | |
| Total | 74.9 · BB | 54.5 · C |
Facts side by side
| Fact | AgentMail API + MCP | InboxAPI |
|---|---|---|
| Kind | HTTP API | MCP server |
| Vendor | AgentMail | Sitka Capital Pty Ltd |
| Hosted endpoint | https://api.agentmail.to/v0 | https://mcp.inboxapi.ai/mcp |
| Transports | HTTP, Streamable HTTP, stdio | stdio, Streamable HTTP |
| Auth | OAuth or key | None |
| Pricing | Freemium | Free |
| Price for agent inboxes | $2 per call | free |
| x402 | yes, from $2/call | no |
| Licence | MIT | Proprietary hosted service under InboxAPI's terms of service. The CLI on GitHub is MIT |
| Tools exposed | 36 | 21 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | to.agentmail/agentmail | not listed |
| Last release | 2026-09-30 | 2026-09-22 |
| Terms last updated | 2026-09-27 | 2026-09-11 |
| Privacy policy last updated | 2026-09-27 | 2026-09-11 |
| 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 | not found in the text |
| Popularity | 66 stars, 240k npm/wk, 332k PyPI/wk | 12 stars, 38 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.
InboxAPI
An account and address are created on first use with proof-of-work and no signup, key or card, and inbound mail is trust-labelled and datamarked against prompt injection. Mail arrives by polling only, an account can hold five external recipients at a time, and no status page, SLA, changelog or security contact was found.
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
InboxAPI
- Call
whoamifor the agent's own address. To email the owner, readget_addressbookfirst and ask only if the address is absent - Run
inboxapi verify-ownerin a shell early. Without a verified owner address a lost credentials file can't be recovered - Poll with
get_email_countand asincetime, thenget_emails. Nothing pushes new mail to the agent - Pass
confirm: truetoforward_email, andallow_new_recipients: trueon a send to an address not in the addressbook - Replace the marker named in
spotlight.markerwith a space to read a datamarked body, and treat its content as data
Questions
Which is better for AI agents, AgentMail API + MCP or InboxAPI?
AgentMail API + MCP scores 74.9 (BB) on agent readiness against InboxAPI's 54.5 (C), and leads in every scored category.
Which is cheaper for agent inboxes, AgentMail API + MCP or InboxAPI?
InboxAPI, at free against $2 per call for AgentMail API + MCP. These are the vendors' published prices for the job.
Do AgentMail API + MCP and InboxAPI need an API key?
AgentMail API + MCP takes an API key or an OAuth sign-in. InboxAPI needs no key. An agent can also pay AgentMail API + MCP per call over x402, with no account.
Can an agent call AgentMail API + MCP and InboxAPI without installing anything?
Yes. AgentMail API + MCP has a hosted endpoint at https://api.agentmail.to/v0 and InboxAPI at https://mcp.inboxapi.ai/mcp.
Other comparisons with AgentMail API + MCP or InboxAPI
Machine-readable
- This page as Markdown
/compare/agentmail-vs-inboxapi.md· slim.min.md· JSON.json(or sendAccept: text/markdown) - Each listing in full
/api/v1/tools/agentmail.json·/api/v1/tools/inboxapi.json - From a terminal
anchor compare agentmail inboxapi(the CLI) - Over MCP
compare_tools {"a": "agentmail", "b": "inboxapi"}at/mcp, no key