Any email I get pops up a notification in the upper-right corner of my screen, as per the native notification settings in the Apple Mail app. Every now and then I will get a quick notification indicating a new email, but then the email notification (and email) will quickly disappear. It's almost as if it was "recalled" by the email server and removed from my machine.
I haven't been able to find any consistency in the type of email that is received - I usually only get a glimpse of who sent it (always a company, never a personal one, at least not that I've noticed) and it's not like the ones that disappear are always from the same place or anything.
The emails in question are from one of my gmail accounts. I have no filters or manually-added spam blockers or blacklisted emails set up in that account, and I've got the email set up with IMAP into Apple's Mail client.
Anyone seen anything like this before? Any ideas of how to stop having these emails disappear?