Best of · Communication
Best email inbox APIs for AI agents
All 7 ranked email inbox APIs on the Anchor benchmark, with a pick for each need and where each one falls short. Scores come from public evidence, re-checked as vendors change.
- 7 ranked
- 1 agent-ready
- 1 accept x402
- 7 hosted endpoints
- Updated 9 October 2026
Top three
Picks by need
Worked out from the scores, prices and facts, so they change when the research does.
Schema & documentation
90/100 on schema & documentation, against 85 for the overall leader.
Security & auth
76/100 on security & auth, against 62 for the overall leader.
Transparency & trust
73/100 on transparency & trust, against 68 for the overall leader.
The shortlist
| # | Tool | Grade | Best for | Price | Where |
|---|---|---|---|---|---|
| 1 | AgentMail API + MCP AgentMail |
BB 74.9 | Agents that need their own address and carry email threads over days, including support, scheduling and outreach agents. | $2 / call | hosted and local |
| 2 | Robotomail Tiny Bot Labs Limited |
B 69.8 | A developer who wants one mailbox per agent with replies as events, on a small fixed monthly price. | $19 / mo | hosted |
| 3 | MailSlurp Pettman OÜ |
B 68.4 | QA and test agents that read OTP, verification and reset mail, and for supervised support agents where a person approves drafts. | $19.99 / mo | hosted |
| 4 | mails.ai Agent Email Mails.ai |
B 66.7 | Agents that send transactional mail and read replies, such as support, notification and verification agents, where an injection score on inbound mail is wanted out of the box. | $20 / mo | hosted and local |
| 5 | Inbound Exon Enterprise LLC |
B 63.7 | A team that wants agent addresses on its own domain at a low fixed price, with IMAP and SMTP beside the API and an MCP mode that confines an agent to one mailbox. | $9 / mo | hosted |
| 6 | Cherami Cherami |
C 57.6 | A single developer or small team giving an agent a free, separate address for low-volume recurring correspondence such as supplier replies, project updates and agent-to-agent handoffs. | Free | hosted |
| 7 | InboxAPI Sitka Capital Pty Ltd |
C 54.5 | A personal mailbox for one coding agent that needs to exchange mail with its owner and a few contacts at no cost. | Free | hosted and local |
How to choose
- How replies reach the agentCheck whether replies arrive by webhook, websocket or polling, since polling adds delay and cost to every check, and a webhook needs a public endpoint.
- Inbox creation and isolationCheck how an inbox is created and whether each can be isolated from others, since an agent that spawns many inboxes must keep their mail apart.
- Thread retention and matchingCheck how long threads are retained and whether replies are matched to their original conversation, since an agent resuming after days needs its earlier messages still stored.
- Prompt injection screeningCheck whether inbound messages are scanned for prompt injection before the agent reads them, since an email body is untrusted text that can carry instructions aimed at the agent.
Each one in detail
AgentMail API + MCP
BB 74.9/100Email inboxes for agents over REST.
Verdict 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.
Choose it for Agents that need their own address and carry email threads over days, including support, scheduling and outreach agents.
Strengths
- Inbox creation, threads, drafts and labels built for agents, with
extracted_textthat drops quoted history - x402 on its own domain and an agent sign-up API, so an agent can start without a person in a dashboard
- Free plan with 3 inboxes and 3,000 emails a month, no card
Weaknesses
- Email sending was down for 8 hours 7 minutes on 19 August 2026
- API request limits aren't published as numbers
- The hosted MCP server's 38 tools load at once, with filtering only in the stdio bridges
Price $2 / callAuth OAuth or keyx402 yeshosted and local
Robotomail
B 69.8/100Robotomail gives an AI agent its own email address for sending, receiving and replying. Access is by REST API, a hosted MCP server with OAuth, a CLI and SDKs, and replies arrive by webhook, SSE or polling.
Verdict A public OpenAPI 3.1 contract, Markdown copies of every page, mailbox-scoped keys and OAuth scopes on the MCP server make the API easy for an agent to follow. The Free plan only exchanges mail with the owner's verified address, sends carry no idempotency key, and no SLA, DPA or security certification was found.
Choose it for A developer who wants one mailbox per agent with replies as events, on a small fixed monthly price.
Strengths
- OpenAPI 3.1 at
/openapi.jsonwith 40 operations, plusllms.txtand a Markdown copy of every public page - API keys can be limited to named mailboxes, and the MCP server takes OAuth with separate
mail:readandmail:sendscopes - Replies reach the agent by signed webhook, by SSE at
GET /v1/eventswith replay, or by polling
Weaknesses
- The Free plan allows 10 sends and 10 receives a month, only with the owner's verified address, and discards other inbound mail
- Sends take no idempotency key, and the SDKs don't retry them, so an uncertain send has to be checked by hand
- No SLA, DPA, SOC 2 or ISO 27001 statement and no bug bounty were found on the site
Price $19 / moAuth OAuth or keyx402 nohosted
MailSlurp
B 68.4/100MailSlurp is a hosted email and SMS API from Pettman OÜ of Estonia. It creates real inboxes and phone numbers for tests and for supervised AI agents, reached over REST, SDKs, IMAP and SMTP, and a hosted MCP server.
Verdict 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.
Choose it for QA and test agents that read OTP, verification and reset mail, and for supervised support agents where a person approves drafts.
Strengths
- Five agent roles from
AGENT_READ_ONLYtoAGENT_SUPPORT, each limited to chosen inbox IDs, inbox tags or the whole account AGENT_DRAFT_ONLYlets an agent write drafts that a person reviews and sends from a review queue- The hosted MCP server takes OAuth with client registration, so no key is pasted into the client
Weaknesses
- 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
- The account API key is also accepted as an
?apiKey=query parameter - The OpenAPI file documents only 2xx responses, and 339 of 844 operations have no description
Price $19.99 / moAuth OAuth or keyx402 nohosted
mails.ai Agent Email
B 66.7/100Hosted email API that gives each AI agent its own address to send, receive and thread mail, with a prompt-injection scan on every inbound message. Reached over REST, TypeScript and Python SDKs, and an MCP server.
Verdict Per-agent addresses with scoped, agent-bound keys, an OpenAPI spec and a prompt-injection score on every inbound message. The operator is unnamed, the vendor calls itself pre-launch, and the status page shows 98.49 per cent API uptime over 90 days with no incident reports.
Choose it for Agents that send transactional mail and read replies, such as support, notification and verification agents, where an injection score on inbound mail is wanted out of the box.
Strengths
- API keys scoped to send, read or manage, bindable to one agent, with expiry and immediate revocation
- Every inbound message carries an injection score and a quarantined flag
- OpenAPI 3.1 spec with 57 operations, llms.txt, an errors page and documented rate limits
Weaknesses
- No company or person named; legal entity details only on request
- 98.490 per cent API uptime over 90 days on status.mails.ai, with no incident reports
- MCP tools carry no readOnly or destructive hints, and MCP errors drop the error code
Price $20 / moAuth API keyx402 nohosted and local
Inbound
B 63.7/100Inbound is an email API from Exon Enterprise LLC for sending, receiving and replying on a customer's own domains. Agents use its REST API, webhooks, scoped IMAP and SMTP mailboxes, a hosted MCP server and the inboundctl CLI.
Verdict A mailbox password limits an agent to chosen addresses and one sending identity across REST, IMAP, SMTP and MCP, and the platform's source is public under MIT. There is no free plan, sign-up needs a browser, webhooks are verified with a static token and are not retried automatically, and no changelog, DPA or security contact was found.
Choose it for A team that wants agent addresses on its own domain at a low fixed price, with IMAP and SMTP beside the API and an MCP mode that confines an agent to one mailbox.
Strengths
- Mailbox credentials scope reading to chosen addresses or domains and sending to one identity, and the same password works over REST, IMAP, SMTP and MCP
- Public OpenAPI 3.1 document with 54 operations, plus
llms.txt,llms-full.txtand Markdown copies of every docs page - The hosted MCP server takes OAuth with PKCE and dynamic client registration, marks every tool with read-only and destructive hints, and narrows its 50 tools with
?toolsets=
Weaknesses
- No free plan or trial on the pricing page. Plans start at $9 a month and the free plan was retired on 3 December 2025
- Webhooks carry a static
X-Webhook-Verification-Tokenheader, not a signature, and failed deliveries are not retried automatically - Account API keys and OAuth tokens (scope
inbound:account) grant the whole account. Only mailbox passwords are scoped
Price $9 / moAuth OAuth or keyx402 nohosted
Cherami
C 57.6/100Cherami gives an agent free @cherami.to email inboxes for recurring correspondence, reached through a hosted MCP server, an HTTP API with an OpenAPI contract, and TypeScript and Python SDKs. A person approves access in the browser.
Verdict Free @cherami.to inboxes with a typed OpenAPI contract, 39 annotated MCP tools and idempotency keys on every send. It's a two-week-old service run by one person, with no status page, no webhooks and keys that reach every inbox on the account.
Choose it for A single developer or small team giving an agent a free, separate address for low-volume recurring correspondence such as supplier replies, project updates and agent-to-agent handoffs.
Strengths
- OpenAPI 3.1 contract with 39 operations, llms.txt and a Markdown twin of every docs page
- Every MCP tool carries readOnly, destructive, idempotent and openWorld hints
- Idempotency keys on sends, replies, forwards and creation, plus a per-operation retry table
Weaknesses
- No status page, SLA or public changelog
- Every API key and OAuth grant reaches all inboxes on the account, with one full-access scope
- No webhooks, so an agent has to poll for new mail
Price FreeAuth OAuth or keyx402 nohosted
InboxAPI
C 54.5/100InboxAPI gives an AI agent its own email address on a subdomain of inboxapi.ai for sending, receiving, searching, replying and forwarding. Access is through MCP, by a local CLI that bridges stdio to the hosted service.
Verdict 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.
Choose it for A personal mailbox for one coding agent that needs to exchange mail with its owner and a few contacts at no cost.
Strengths
- First use creates the account and address by proof-of-work, with no signup form, API key or card
- Every inbound message carries a trust level, and untrusted bodies and subjects are datamarked with a per-request marker
- The CLI hides nine auth and encryption tools from the model and requires
confirmonforward_email
Weaknesses
- Mail arrives by polling only. No webhook, websocket or push tool was found in the tool list or docs
- An account holds five external recipient slots, and a full slot frees only after five days without use
- No status page, SLA, changelog, security.txt or disclosure policy was found on the site or in the repository
Price FreeAuth Nonex402 nohosted and local
Head to head
- AgentMail API + MCP vs Robotomail BB 74.9 vs B 69.8
- AgentMail API + MCP vs MailSlurp BB 74.9 vs B 68.4
- AgentMail API + MCP vs mails.ai Agent Email BB 74.9 vs B 66.7
- AgentMail API + MCP vs Inbound BB 74.9 vs B 63.7
- MailSlurp vs Robotomail B 68.4 vs B 69.8
- mails.ai Agent Email vs Robotomail B 66.7 vs B 69.8
- Inbound vs Robotomail B 63.7 vs B 69.8
- mails.ai Agent Email vs MailSlurp B 66.7 vs B 68.4
- Inbound vs MailSlurp B 63.7 vs B 68.4
- Inbound vs mails.ai Agent Email B 63.7 vs B 66.7
Questions
What are the highest-rated email inbox APIs for AI agents?
AgentMail API + MCP has the highest benchmark score of the 7 ranked email inbox APIs, 74.9 (BB). Robotomail is second with 69.8 (B).
How many email inbox APIs are agent-ready?
1 of the 7 ranked here grade BB or better, the bar for agent-ready on the Anchor benchmark.
Which email inbox APIs accept x402 payments?
AgentMail API + MCP. An agent can pay these per call in USDC with no account.
How is this list ranked?
By the Anchor benchmark score out of 100, a weighted mean of the scored categories minus deductions for negative events, from public evidence re-checked as vendors change. Listings cannot pay for a place. The latest assessment behind this page is from 9 October 2026.
How this list is made
The order is the Anchor benchmark score, the same number as on each listing and in the top list. Each listing is graded from public evidence against the benchmark checklist, and the picks above are worked out from those grades, prices and facts. No listing pays for its place, and paid audits or listing help never change a score.
Full ranked table · 21 head-to-head comparisons · Best tools in every category