kumomta/docs/reference/headermap/set_content_transfer_encoding.md

set_content_transfer_encoding

headers:set_content_transfer_encoding(VALUE)

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

Assign the VALUE to the Content-Transfer-Encoding header.

VALUE may be either a string or be an MimeParams.

If you assign using a string, the string will be parsed and validated as being compatible with MimeParams before allowing the assigment to proceed.

!!! danger Changing the Content-Transfer-Encoding header may result in an inconsistent representation of the message and should be avoided. We recommend limiting changes to just the parameter portion of the header rather than the overall encoding.