When attaching public key, we take the root mime part, create a new root,
and put the old root alongside an additional public key mime part.
But when moving the root, we would copy all content headers, even empty ones.
So we’d be left with Content-Disposition: "" which would fail to parse.
Gluon used to have a bug where it would unnecessarily call the
reporter's ReportMessageWithContext method whenever an IMAP client would
drop unexpectedly. After fixing the bug, we can remove these gomock
EXPECT.AnyTimes() calls.
We should only listen on constants.Host when serving IMAP and SMTP.
This change fixes that. It also adds a test that we can send over SMTP
and receive over IMAP.
