kumomta/docs/reference/mimepart/append_part.md

append_part

mimepart:append_part(PART)

{{since('2025.10.06-5ec871ab')}}

Appends PART, which must also be a MimePart (perhaps created via kumo.mimpart.new_text or similar) to the set of child parts in mimepart.

This is potentially useful when constructing complex multipart messages. You are responsible for ensuring that the resulting mime tree makes logical sense; mimepart should have a Content-Type that is recognized as being a multipart container of some kind.

You might consider instead using kumo.mimepart.builder for a simpler message building experience.