Summary: Ref T13065. See similar changes attached to that task.
Test Plan: Ran migration, got a clean database state, saw mail keys populate in mail property table.
Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam
Maniphest Tasks: T13065, T13641
Differential Revision: https://secure.phabricator.com/D21625
