Start with one question
"Email API" covers three different products, and most bad choices come from picking the wrong one. Before comparing features, decide which of these your agent needs:
- Its own address. The agent is a participant: it signs up for things, writes to customers, chases suppliers, and receives the replies. You want an agent inbox API.
- Somebody else's inbox. The agent works inside a person's existing Gmail or Outlook — triaging, drafting, booking. You want a connected-account API.
- Only to send. Reports, alerts, receipts. Nobody replies, or a reply does not matter. You want a transactional sender.
Most agents that do real work are the first kind, and the first kind is the hardest to build yourself. That is where this list spends most of its time.
Agent inbox APIs
An address created by an API call, mail stored and threaded for you, and an event when something arrives. This is the category built for agents.
1. Pidgeon
Pidgeon gives an agent a real inbox: send, receive, threads, labels, drafts, attachments and a calendar, over a REST API, an MCP server, and IMAP and SMTP. What sets it apart is the person beside the agent: thread ownership (human, agent or automation) is part of the model, with events when it changes, so a person can take a thread over and hand it back. A Firewall verdict on every inbound message names anything trying to instruct the agent.
- Best for: agents whose conversations a person sometimes needs to see or own — support, collections, recruiting, operations.
- Getting started: an agent can sign itself up with two HTTP calls and a six-digit code from a human. Or point your coding agent at
pidgeon.ai/skill.md. - Pricing: unlimited inboxes on every plan; free with your own domain, then €20 or €200 a month for more sending, domains and team members. Receiving is free on every plan.
- Where it differs: mail stored and processed in the EU on every plan, and a Firewall verdict on every inbound message.
2. AgentMail
AgentMail offers inboxes by API, webhooks and WebSockets, SDKs, an MCP server, and framework integrations.
- Pricing: free with 3 inboxes and 3,000 emails a month; $20 a month for 10 inboxes; $200 for 150.
- Trade-off: its EU region is on Enterprise only (pricing). We have compared it with Pidgeon in detail.
Also worth knowing
Nylas Agent Accounts (below) and Resend Inboxes (in private beta) bring agent inboxes to two established email APIs. Several newer agent inbox products have launched in 2026 too — check how long a product has been running and how it handles deliverability before you put customer conversations on it.
Connected-account APIs
For an agent that works inside an inbox somebody already has.
3. Nylas
Nylas is a unified API over Gmail, Microsoft 365 and IMAP providers: one integration, many providers, plus calendar, contacts and meeting notes. It is the right answer when the agent is an assistant to a specific person. Since 2026 it also hosts Agent Accounts, inboxes an agent owns.
- Trade-off: through a connected account the agent borrows a person's address, so everything it sends is in that person's name. See every comparison.
4. Gmail API and Microsoft Graph
Going direct to Gmail or Microsoft Graph gives you the deepest access to one provider.
- Trade-off: a paid seat per inbox, restricted OAuth scopes with an annual security assessment for products that store the data, a push channel that must be renewed every 7 days, and sending caps that lock an account for up to 24 hours when exceeded. Fine for a person's assistant; awkward as an agent's own identity. See Pidgeon vs the Gmail API.
Transactional senders with inbound
Built to send at volume, with inbound offered as a webhook.
5. Resend, Postmark, Amazon SES and Mailgun
All four send reliably and receive mail, posting each message to your endpoint as an event. Resend has the friendliest developer experience; Amazon SES is the cheapest at scale; Postmark is known for transactional deliverability. Resend keeps received mail for 30 days, and is testing an inbox API with threads in private beta. Compared in detail: Pidgeon vs Resend and Pidgeon vs SendGrid.
- Trade-off: inbound is an event, not an inbox — outside Resend's beta. Storing messages, threading replies across clients, search, and showing a person what happened are yours to build. That is a reasonable project — it is also most of what an agent inbox API is.
6. Cloudflare Email
If you already run on Cloudflare Workers, Email Routing hands inbound mail to a Worker and Email Sending sends from one, with no separate API key to manage.
- Trade-off: your domain's DNS must be on Cloudflare, and the inbox — storage, threads, history — is again yours to build.
Self-hosting
Stalwart and Postal are open-source mail servers you can run yourself, with no per-inbox price.
- Trade-off: you take on IP reputation, warm-up, blocklists, DMARC alignment and an on-call rotation for all of it.
Side by side
| Agent owns the address | Mail stored and threaded | A person can open it in a mail client | Best for | |
|---|---|---|---|---|
| Pidgeon | Yes | Yes | Yes, IMAP and SMTP | Agents a person sometimes needs to step in for |
| AgentMail | Yes | Yes | Yes, IMAP and SMTP | Agent inboxes, EU only on Enterprise |
| Nylas | Both | Yes | Yes | An assistant across many providers |
| Gmail API, Microsoft Graph | No — a person's | In the provider | Yes, it is their inbox | An assistant on one provider |
| Resend, Postmark, SES, Mailgun | Sends; inbound by webhook | Resend keeps 30 days | No | Notifications and receipts |
| Cloudflare Email | Yes | No | No | Teams already on Workers |
| Self-hosted | Yes | Yes | Yes | Mail that cannot touch a third party |
What to check before you choose
- Where does a reply go? If the answer is "a webhook", ask where it is stored, how it is matched to the conversation, and who can see it later.
- Can a person step in? Sooner or later a customer writes something your agent should not answer. Check what taking over a thread looks like, and how the agent finds out.
- What can the agent reach? Look for keys scoped to one address and rules about who it may write to, not one key for everything.
- Is inbound treated as untrusted? An email is text from a stranger, delivered straight into your agent's context. Treat it as possible prompt injection, and keep consequential actions behind a check.
- How is it priced? Per inbox, per message or per account changes the answer completely once you have hundreds of agents.
- Can you leave? IMAP, an export, and a domain that stays yours make the next decision cheap.
Our pick
- An agent that needs its own address, and a person may need to read along: Pidgeon.
- Mail that must stay in the EU: Pidgeon, on every plan.
- An assistant inside someone's Gmail or Outlook: Nylas, or the provider's own API for one provider.
- Notifications nobody replies to: Resend, Postmark or SES.
We make Pidgeon. Every claim about another product is sourced to its own pages, checked on 25 October 2026; if one is out of date, write to support@pidgeon.ai and we will fix it.
For the closest alternative side by side, see AgentMail vs Pidgeon, and for the inbox itself, email inboxes for AI agents.