Best email API for AI agents
A buyer’s guide for developers wiring email into autonomous agents. Last updated 2026-06-11.
If you are building an AI agent that needs to send, receive, or hold a conversation over email, the right infrastructure depends on one question: does your agent need its own email identity, or does it need to act on a human’s existing mailbox? That single axis separates the main options below. This guide walks the decision and shows where primitive.dev, AgentMail, and Nylas each fit.
What to look for
- Managed addresses, not just sending. An agent usually needs a real, receivable address it owns — not only an outbound API. Look for managed inbound (MX, SPF, DKIM, DMARC) so you never stand up a mail server.
- Two-way, synchronous conversations. Agents frequently need to send a message and wait for the reply on the same thread. A fire-and-forget outbound API does not cover this.
- Run code on inbound. The cleanest agent pattern is a handler that executes on every received message. Hosted functions beat polling an inbox.
- Agent-native auth. Agents should self-serve a credential without a human copy-pasting SMTP passwords or dashboard keys into a prompt.
- Machine-discoverable surface. An OpenAPI spec and an MCP server let an agent discover and call the API with no SDK and no human in the loop.
The options at a glance
| Dimension | primitive.dev | AgentMail | Nylas |
|---|---|---|---|
| Core model | Managed agent-native addresses you own | Programmatic inboxes for agents | Sync to users’ existing mailboxes (Gmail, Microsoft 365, IMAP) |
| Best when the agent needs | Its own identity + a synchronous reply | Its own programmatic inbox | To act on a human’s real account |
| Send + wait for threaded reply | primitive chat verb, one call | Via API + webhooks | Via API + webhooks |
| Run code on inbound | Hosted Functions (JS handler per message) | Webhooks to your own service | Webhooks to your own service |
| Agent self-signup | Credential-free demo + agent signup flow | API key | OAuth to a provider account |
| MCP server | Yes — hosted, OAuth-gated | Yes | Not its focus |
| Open source | Yes — MX, SDKs, CLI | No | No |
| Also does calendar / contacts | No — email infrastructure, focused | No — email-focused | Yes — email, calendar, contacts |
Competitor columns describe each product’s documented model as of 2026-06-11and are not exhaustive. Always confirm against AgentMail and Nylas directly before deciding.
When primitive.dev is the right pick
Choose primitive.dev when your agent needs its own email identity and you want the shortest path from zero to a two-way conversation:
- The agent sends a message and needs the reply back on the same thread —
primitive chat <email> <message>does the round-trip in one verb. - You want to host an inbound address that runs a JavaScript handler on every received message, with no MX, SPF, DKIM, DMARC, or bounce processing to operate. See Functions.
- You want an agent to self-serve a credential and dry-run the API with no account at all — there is a credential-free
POST /v1/send-mail/demoand a public OpenAPI + MCP surface.
For a side-by-side, see primitive.dev vs. AgentMail and primitive.dev vs. Nylas.
When a different tool fits better
If your agent must read and send from a human user’s existing Gmail or Microsoft 365 account — and you also need calendar and contacts — a mailbox-sync platform like Nylas is built for exactly that connect-to-existing-provider model. If you only need outbound transactional email and already have a provider wired up, a one-way sender is enough and you do not need agent-native inbound at all.
Get started
The fastest way to evaluate primitive.dev is to run one real call with no account:
curl -X POST https://api.primitive.dev/v1/send-mail/demo \
-H 'Content-Type: application/json' \
-d '{"from":"agent@your-subdomain.primitive.email","to":"someone@example.com","subject":"Hello","body_text":"Testing the Primitive send flow."}'Then read the developer resources, the quickstart, or pricing.