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Transactional Email API for AI Agents

OTPs, receipts, and notifications — sent by agents that own their address and their reputation.

A transactional email API for AI agents handles the sends your agents trigger — receipts, confirmations, one-time codes, status updates — from addresses the agents own. Unlike a classic transactional API, the sender here is autonomous: each agent keeps its own identity, thread history, and reputation, and can read the replies.

Transactional sends, agent-shaped

The mechanics look familiar — POST a message, it gets delivered. The difference is the sender model: the agent that triggered the send owns the address, so follow-ups, replies, and threading belong to it rather than to a no-reply void.

curl https://api.mails.ai/v1/messages \
  -H "Authorization: Bearer $MAILS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "agent": "hello",
    "to": "user@example.com",
    "subject": "Receipt for July",
    "body_text": "Your July invoice is settled — total $49.00. Reply if anything looks off."
  }'

Reliability from posture, not promises

Deliverability on shared rails is mostly determined by your neighbors. This platform checks every send before it leaves and manages reputation per agent, so transactional traffic rides a clean rail. A low-volume agent can run on the free tier — 3,000 emails and 3,000 inbound replies a month — and Pro is $20 a month for 50,000 emails and 50,000 inbound replies.

For the complete send-and-receive picture, see the email API for AI agents overview — it covers inbound events, prompt-injection scoring, and code examples in both TypeScript and Python.

Frequently asked questions

How is this different from SendGrid, Postmark, or Resend?
Classic transactional APIs model one application sending fire-and-forget mail from a shared identity. Here the unit is the agent: each one has its own address and reputation, and receiving is first-class — replies come back as parsed, injection-scanned events the agent can act on. There are migration guides from each of those platforms.
Can I use drafts for human review before an agent sends?
Yes — create a draft, let a human (or a second agent) edit or approve it, then POST /v1/drafts/{id}/send. Useful when transactional sends carry judgment, like refund notices.
Is cold outreach allowed on this rail?
No — cold email is prohibited by the acceptable-use policy and blocked at the API. That posture is deliberate: it keeps the shared infrastructure clean, which is why routine transactional mail from agents here inboxes reliably.

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Give your first agent an inbox

Free covers 3,000 emails and 3,000 inbound replies a month, with no card. Upgrade when your agents get busy.

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