kumomta/docs/reference/message/set_sender.md

message:set_sender(ENVELOPE)

{{since('2023.08.22-4d895015')}}

Sets the envelope sender of the message. The value can be an EnvelopeAddress or a string that can be parsed into an EnvelopeAddress.

message:set_sender(string.format('bounce-%s@%s', HASH, DOMAIN))

See also message:set_recipient.