Phabricator seems to send empty emails like the following fairly often:
> REPOSITORY
> rL LLVM
>
> http://reviews.llvm.org/D9775
>
> EMAIL PREFERENCES
> http://reviews.llvm.org/settings/panel/emailpreferences/
I'm told this happens "for things like closing a revision, adding dependencies or subscribers". These emails should either say what they're for or not be sent at all.
Some discussion here: http://lists.cs.uiuc.edu/pipermail/llvmdev/2015-May/085869.html