This is a bit of a strange twist in the spirit of "Phabricator sends too much mail" and I'm afraid it will be lacking reliable reproduction steps, as I can't figure any out yet. However, I think it may be worth starting the conversation in case others have experienced this, and perhaps through conversation and further investigation we as a community can figure out how to reproduce it.
The issue is this: Sometimes Phabricator seems to send mail when it shouldn't.
We prepared user accounts for some of our users and began using them, e.g. assigning tasks to them, before they validated their email addresses, yet Phabricator occasionally sent them mail. Mostly it didn't, but sometimes it did. I think the most commonly sent mails were "Block/Unblock" notifications, but don't think they were the only ones.
- Sometimes Phabricator sends emails despite your email preferences. For example, I have opted not to receive emails about column changes, yet sometimes I receive emails notifying me about column changes (and only column changes).
It seems very strange, and I can't fathom what could be causing it, nor do I have enough experience with Phabricator yet to really know how to investigate it further.
It's been happening for at least about a year, I'd say. Currently my instance is running these versions which aren't cutting edge, but aren't all that old either:
phabricator 27006fedccc2f487dcaf7177f6d127ccd0e6df7d (Sep 24 2016) arcanist e7906e47cba2006fa46553d462abf1f685845f20 (Sep 24 2016) phutil 518dacd785fb19d67643e4a113e99b8825a87f99 (Sep 24 2016)