SMTP Relay

HTTP-based SMTP relay. Accepts raw RFC 822 MIME or a simple envelope. Pair with any SMTP-to-HTTP sidecar for true SMTP over TCP.

Endpoint

POST /smtp/send

Scopes: emails:send

Option A — raw MIME

For sidecar proxies that already have a parsed RFC 822 message:

body

{
  "raw": "From: hello@yourdomain.com\r\nTo: user@example.com\r\nSubject: Hi\r\n\r\nHello there"
}

Mailgrid parses headers (From, To, Subject, Content-Type) and routes through the standard send() path. All suppression, idempotency, tracking, and stream rules apply.

Option B — JSON envelope

For lighter-weight clients:

body

{
  "envelope": {
    "from": "hello@yourdomain.com",
    "to": ["user@example.com"],
    "subject": "Hi",
    "text": "Hello there"
  }
}

Response

202 Accepted

{
  "success": true,
  "data": {
    "smtpCode":    250,
    "smtpMessage": "OK 0107019a-...",
    "messageId":   "0107019a-...",
    "status":      "sent"
  }
}

True SMTP over TCP

Cloudflare Workers can't listen on TCP — that's a platform constraint. For legacy clients that need SMTP on port 25 or 587, run a small sidecar that translates SMTP to HTTP POSTs. See the SMTP sidecar guide.