Comment 6 for bug 1801163

I've tested and pushed a signoff to user/gmcharlt/lp1801163_email_mime_signoff.

The signoff branch contains two follow-ups:

[1] Adding the new dependencies to the Buster and Fedora installation. I've not actually tested the Fedora part, though.
[2] Ensure that non-ASCII characters in the headers don't get mangled.

Since without this bugfix SendEmail appears to be completely broken on (at least) Debian Stretch and later and Ubuntu 18.04 and later, I think we'll need to bite the bullet and backport this.