Add the option to tune the "DKIM-Signature" header
According with RFC 8058 "Signaling One-Click Functionality for List Email Headers" (https://tools.ietf.org/html/rfc8058) in order to use the header "List-Unsubscribe" this must be included on "h" tag of DKIM sign, nowadays only "From:To:Subject;" are included on DKIM-Signature.
The idea is to allow the option to include additional information on the Plesk generated "DKIM-Signature" "h" tag.
Thank you for your input! We will consider this functionality in upcoming releases if it will be popular.
Everyone, please continue voting for this feature if you consider it important.