Accept case-insensitive mail replies

Summary:
Mailbox sometimes (?) changes the case of the email address (?). Be more liberal in what we accept.

Also fix a minor output bug.

Test Plan: Sent mail to `e1+...` instead of `E1+...`, verified it arrived.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D7575