`message:set_data(payload)`

Since: Version 2024.06.10-84e84b89

The functionality described in this section requires version 2024.06.10-84e84b89 of KumoMTA, or a more recent version.

Replaces the message body/data completely. It is your responsibility to ensure that the content is well-formed, has canonical CRLF line endings, and uses appropriate transfer-encoding, otherwise the system will misbehave when delivering the message.