The approach introduced in commit d88e3624ea4 (see bug 1031335) to MIME-encode headers does not work when using recent versions of Encode::MIME::Header. Specifically, Encode::MIME::Header 2.22 or later, which is part of Encode 2.83 or later, adopts a much stricter view of its task and does not work for structured header fields like To or From.
In particular, older versions of Encode::MIME::Header would yield results like this:
From: stuff <email address hidden>
while newer version give you something like
From: =?UTF-8?B?c3R1ZmYgPGZvb0BiYXIuY29t?=
Email::Send chokes on the latter when it tries to determine the sender address to use for the SMTP transaction.
Since the maintainers of Encode::MIME::Header are unwilling (see https://github.com/dankogai/p5-encode/issues/105) to make it handle structured headers in a more "bug-compatible" fashion, we'll need to do something else. Email::MIME or Email::Stuffer both look promising.
Marking this high importance because it's evident that there's at least one case where an innocent upgrade of Encode results in breaking outgoing A/T email.
Evergreen 3.1+
I want to point out related bug 1466502, and bug 1362260 which took the approach of installing Email::Send from CPAN.
Perhaps an alternate solution is to finally switch to Email::Sender?