R1:e808963eae75

Add Ponder Question mail create receiver

Summary: Fixes T11115, but unclear how to test this. I think I've asked this in the past.

Test Plan:
- Visit Applications -> Ponder
- Configure external email
- Test External Email
- See new Question

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11115

Differential Revision: https://secure.phabricator.com/D16084