We always had the notifications set for "Perodic" but in the past ( Two Months ago), the Mentions would show up immediately and the other notifications based on card membership etc would arrive once or twice a day. Now we never recievie the mentions at all. The mail notifications work for everything else just as they always have.
All was working as recent as Feb but now nothing. I have change the notification settings several times, no difference. I now have it set to deliver Immediately plus enabled desktop notifications. The Desktop Notifications work but still no emails for Mentions.