Summary: Fixes T1144. Though actually I think T1144 wanted some handy way to email from the command-line / arc, this is cooler. :D
Test Plan: set conf properly and then ./bin/mail receive-test --as btrahan --to pasties@phabricator.dev | README --> it worked...! couldn't test files as easily but verified exception thrown when I tried to test.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T1144
Differential Revision: https://secure.phabricator.com/D6622
