Previously the email gateway had to be the only address in a recipient
field or we'd mis-parse the recipient.
This commit also makes the mirror correctly handle addresses of the
form "Jessica McKellar <jesstess@zulip.com>".
(imported from commit 7435f2b59b8f47dc599cc869f64597a730af7d12)
The mirror will use INBOX when deployed and Test locally. Send an
e-mail to the Test mailbox by including the word "localhost" in the
subject; a GMail filter will place it in Test on receipt.
(imported from commit bacf9a9554c8c5e1f3ec8497761edf2c15d3745d)
For now, just do this, and we'll reach out to realms having trouble
manually. We may eventually need to automatically reply to the e-mail,
reach out to a realm admin, etc.
(imported from commit 5c5ac354066f9e9be3fb928e1f8801613c22c1ac)
