Forward an email message from an AgentMail inbox to new recipients via API.
What it does
This endpoint is part of the AgentMail MPP gateway, which provides programmatic email inboxes designed for AI agents. The Forward Message endpoint (`POST /v0/inboxes/{inbox_id}/messages/{message_id}/forward`) takes an existing message in an inbox and forwards it to one or more new recipients. The request body accepts `to`, `cc`, `bcc`, `subject`, `text`, `html`, `headers`, `reply_to`, `labels`, and `attachments` fields, following the same `SendMessageRequest` schema used by the send-message endpoint. On success it returns a `SendMessageResponse` containing the new `message_id` and `thread_id`.
The endpoint is served over the MPP (Micropayment Protocol) at `https://mpp.api.agentmail.to` and is priced at a fixed $0.01 per call according to the OpenAPI `x-payment-info` annotation. Authentication is via Bearer token in the `Authorization` header. The broader AgentMail API also supports creating inboxes ($2.00), sending messages ($0.01), replying ($0.01), managing drafts, threads, domains, webhooks, allow/block lists, and querying metrics — all accessible through the same MPP gateway.
Note: the probe did not capture a live 402 MPP challenge on this specific endpoint (it returned 404 on HEAD/GET, which is expected since the operation is POST-only). The OpenAPI spec is comprehensive and the root landing page is live, so the endpoint is presumed operational when called with POST and valid path parameters.
Capabilities
Use cases
- —AI agent forwards a received email to a human supervisor for review
- —Automated workflow redistributes inbound messages to different team members
- —Agent triages support emails and forwards them to the appropriate department
- —Bot forwards confirmation emails to an external system's inbox
- —Multi-agent pipeline passes email context between specialized agents
Fit
Best for
- —AI agents that need their own email addresses and can forward messages programmatically
- —Automated email triage and routing workflows
- —Developers building agent-to-human email communication pipelines
Not for
- —Bulk marketing email campaigns (this is per-message, not bulk-optimized)
- —Reading or managing a human user's existing Gmail/Outlook inbox
Quick start
curl -X POST 'https://mpp.api.agentmail.to/v0/inboxes/{inbox_id}/messages/{message_id}/forward' \
-H 'Authorization: Bearer YOUR_TOKEN' \
-H 'Content-Type: application/json' \
-d '{"to": "recipient@example.com", "text": "FYI — forwarding this to you."}'Example
Request
{
"cc": "manager@example.com",
"to": "colleague@example.com",
"html": "<p>Please see the forwarded message below.</p>",
"text": "Please see the forwarded message below.",
"subject": "Fwd: Original subject"
}Response
{
"thread_id": "thr_xyz789",
"message_id": "msg_abc123"
}Endpoint
Quality
Full OpenAPI 3.1 spec with detailed schemas and x-payment-info pricing is available. However, the probe did not capture a live 402 MPP challenge on this POST-only endpoint (HEAD/GET returned 404 as expected), so liveness is inferred rather than confirmed. No standalone docs page was reachable on the MPP subdomain.
Warnings
- —Probe returned 404 on HEAD/GET because this is a POST-only endpoint; liveness not directly confirmed via 402 challenge
- —No dedicated documentation page found at the MPP gateway origin — docs are at docs.agentmail.to
- —Price ($0.01) is taken from x-payment-info in the OpenAPI spec; actual MPP challenge was not captured to cross-verify
Citations
- —Forward Message endpoint is POST /v0/inboxes/{inbox_id}/messages/{message_id}/forward with fixed price 0.01https://mpp.api.agentmail.to
- —AgentMail is the email inbox API for AI agents, raised $6M in seed fundinghttps://mpp.api.agentmail.to
- —Response schema is SendMessageResponse with message_id and thread_idhttps://mpp.api.agentmail.to
- —Create Inbox costs $2.00, Send/Reply/Forward cost $0.01 each per x-payment-infohttps://mpp.api.agentmail.to