Some of this stuff has other tasks, but the general issues with Maniphest email that I'm expecting to fix in the next pass are:
- We ninja vanish email we can't figure out, out of fear of creating email loops if we reply to it, but should get over this and send you an error if we can't handle your message.
- CCs from the original email should transfer to the task, insofar as we can identify accounts, if they don't already.
- Project hashtags (`#qa`) in the mail body should imply assignment.
- The "MAIL ACTIONS" header is missing from the mail we send right now, so users have no way to figure out that they can reply or which actions are available.
- It should be more clear that `!action` statements must appear on the first line, or we should be more liberal about where they're allowed to appear.
- Now that we have custom statuses and suffixes, we could let `!close` take optional suffixes.