set_content_type
Since: Dev Builds Only
The functionality described in this section requires a dev build of KumoMTA. You can obtain a dev build by following the instructions in the Installation section.
Assign the VALUE to the Content-Type 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.