Send a message from a mailbox

Compose and send a NEW message from a hosted mailbox — a first email to someone, not a reply inside a thread that already exists. It goes out from the mailbox's own address, over its own domain, and the recipient can reply to it.

The sender is the mailbox in the path. There is no from field: a route that sends under a customer's own identity must not take the identity as an argument.

Supply either body (plain text) or document (a branded React Email document with images, GIFs, buttons and columns). Sendly renders both HTML and a matching text alternative. Caller HTML, JSX and arbitrary CSS are not accepted.

Bcc recipients are delivered to but appear in no header, which also means the copy filed in the mailbox's Sent folder does not record them.

Refusals worth handling by name:

• 422 RECIPIENT_SUPPRESSED — one or more recipients are on this project's suppression list. The message names them; remove them or take them off the list.
• 422 CONTENT_REFUSED — the outbound content scanner refused the message.
• 503 CONTENT_SCAN_UNAVAILABLE — screening could not reach a verdict for a young project. Nothing was sent; retry shortly.
• 429 — a mailbox may send 60 messages an hour through this endpoint.

The message is stored as a new conversation on the mailbox, so the reply threads onto it.

Requires the mailboxes:send scope — Write and send new email from your hosted mailboxes, as that address.