Message could not be parsed

message.unparsable · HTTP 400

What it means

The injected message could not be read as an email: its headers or structure are not valid, or reading it took too long. Nothing was stored.

What to do

Send the message exactly as it would follow the SMTP DATA command: headers, a blank line, then the body, with Content-Type: message/rfc822. Save a message your mail client or library produces and send that file to check.

Every error the API returns is a JSON problem (RFC 9457) whose code names it and whose type links to its page here. See the docs for how the API works.