Message too large

message.too_large · HTTP 413

What it means

The injected message is larger than 10 MB, the same limit mail meets on port 25, so it was not stored.

What to do

Send a smaller message: remove or shrink attachments. Test fixtures rarely need more than a few kilobytes.

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.