Send a previously created email draft from an AgentMail inbox via the MPP payment protocol.
What it does
This endpoint is part of the AgentMail MPP gateway, which provides email inbox infrastructure for AI agents. The "Send Draft" operation (`POST /v0/inboxes/{inbox_id}/drafts/{draft_id}/send`) takes a previously created draft in a specific inbox and sends it as an email. It accepts an optional request body to add or remove labels on the message at send time. On success it returns the resulting `message_id` and `thread_id`.
AgentMail's broader API lets agents create inboxes, compose drafts, send and receive messages, manage threads, handle attachments, configure webhooks, and operate custom domains — all via REST. The MPP gateway wraps these operations behind the Machine Payment Protocol so AI agents can pay per call. The Send Draft endpoint is priced at a fixed $0.01 per call according to the OpenAPI `x-payment-info` field. Other related operations such as creating inboxes ($2.00), creating domains ($10.00), and sending messages ($0.01) are also available on the same gateway.
Authentication is via Bearer token in the `Authorization` header. The endpoint may return 400 (validation error), 402 (payment required), 403 (forbidden), or 404 (not found). Note that the probe returned 404 when tested with HEAD/GET, which is expected since this is a POST-only endpoint.
Capabilities
Use cases
- —AI agent sends a composed draft email to external recipients
- —Automated workflow finalizes and dispatches a prepared email draft
- —Agent schedules and then triggers sending of a pre-built message
- —Bot replies to inbound emails by creating and sending drafts
Fit
Best for
- —AI agents that need their own email inboxes and outbound sending
- —Automated email workflows where drafts are composed then sent separately
- —Applications requiring per-call paid email sending without monthly subscriptions
Not for
- —Bulk marketing email campaigns (no evidence of bulk-send support)
- —Human-facing email clients or webmail interfaces
- —Reading or searching existing personal email accounts (this creates new agent inboxes)
Quick start
curl -X POST https://mpp.api.agentmail.to/v0/inboxes/{inbox_id}/drafts/{draft_id}/send \
-H "Authorization: Bearer $TOKEN" \
-H "Content-Type: application/json" \
-d '{}'Example
Request
{
"add_labels": [
"sent"
],
"remove_labels": [
"draft"
]
}Response
{
"thread_id": "thr_xyz789",
"message_id": "msg_abc123"
}Endpoint
Quality
Full OpenAPI 3.1 schema with detailed component definitions and clear x-payment-info pricing. The specific endpoint is POST-only so the 404 on HEAD/GET probes is expected, not a liveness failure. Docs pages on the MPP gateway return 404, so external documentation is thin; however the OpenAPI spec itself is comprehensive.
Warnings
- —Probe returned 404 because HEAD/GET were used on a POST-only endpoint; endpoint is likely live but could not be confirmed with a 402 challenge.
- —No dedicated documentation pages found on the MPP gateway (docs/api/pricing all return 'Endpoint not found').
- —Price field in x-payment-info is '0.010000' but the currency/token is not explicitly stated in the OpenAPI spec; assumed USD based on context.
Citations
- —Send Draft endpoint is POST to /v0/inboxes/{inbox_id}/drafts/{draft_id}/send with fixed price 0.010000https://mpp.api.agentmail.to
- —Response schema returns message_id and thread_id (SendMessageResponse)https://mpp.api.agentmail.to
- —Request body accepts UpdateMessageRequest with add_labels and remove_labelshttps://mpp.api.agentmail.to
- —AgentMail is the email inbox API for AI agents, raised $6M seed fundinghttps://mpp.api.agentmail.to
- —Creating an inbox costs $2.00 and creating a domain costs $10.00 per the x-payment-info fieldshttps://mpp.api.agentmail.to