Summary: This keeps people in the correct To or CC field on multiplexed messages.
Test Plan:
with multiplexing on, checked that I received an email with me in the CC
field instead of the To field for a diff I'm CC'd on.
Reviewers: epriestley, jungejason, vrana
Reviewed By: epriestley
CC: aran, Korvin
Differential Revision: https://secure.phabricator.com/D2999
67c302ae4f