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Questions · Published 2026-11-09 · Updated 2026-11-09 · AgentiSend

What is a transactional email API?

A transactional email API accepts one message over HTTP, such as a receipt or a password reset, and returns an id.

A transactional email API accepts one message over HTTP, such as a receipt or a password reset, and returns an id. AgentiSend is that API: the call is POST /emails, the follow-up is GET /emails/{id}, and the record of what the receiving server did is GET /emails/{id}/events.

The request and the response

The body is the address you send from, who it is for, the subject, and the text or HTML. The response is the id of the message AgentiSend accepted.

curl -sS -X POST https://api.agentisend.com/emails \
  -H "Authorization: Bearer $AGENTISEND_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"from":"billing@yourdomain.com","to":"delivered@simulator.agentisend.com","subject":"Your receipt","text":"Thanks — the details are attached."}'
201
{
  "id": "9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42",
  "simulated": true,
  "warnings": []
}
Response

GET /emails/{id} returns that message and its status. To hear about it without polling, POST /webhooks subscribes an HTTPS endpoint to the event types you name.

The four delivery events

These four are the delivery record. Each sentence is the event catalogue, which is generated from the list the API emits. The rest of the catalogue, including opens, clicks and delays, is Events.

  • email.sent: AgentiSend hands the message off for delivery, or a send to a simulator address is answered without leaving AgentiSend.
  • email.delivered: The receiving mail server accepts the message.
  • email.bounced: The receiving server rejects the message for a recipient, during delivery or in a bounce report mailed back afterwards.
  • email.complained: A recipient marks the message as spam and their mailbox provider reports it back.

delivered means the receiving server accepted the message. It does not mean a person opened it, and it does not name the folder.

When not to use one

Do not use a transactional email API for unsolicited mail. AgentiSend refuses cold outreach: there is no lead database and no import of addresses nobody asked for.

Do not use one when the job is an inbox and an identity per agent. That comparison is AgentiSend vs AgentMail. Receiving mail you were sent, at your own domain, is a different call and is described on Can an AI agent receive email?.

Do not use one when the only path you have is SMTP submission. AgentiSend sends over HTTP. The product page with the free number and the plan ladder is Email API.

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