No formal decision there, and the stdlib API seems like a PITA as it's
based around native strings, not bytes and not text.
* try to use cross-model API instead of random encode/decode
* unicode all the mail_template things
* formataddr *requires* a text tuple now
In P2, formataddr((False, False)) "worked" (generated "False
<False>"), in P3 it will fail and blow up.
* attachments are quite definitely bytes
* remove try_coerce_ascii because it's garbage