I noticed I haven't been getting email notifications of people finding my caches lately. I have been getting published and watch list notifications though. I checked the Groundspeak forums and it seems that this is a recent problem for Gmail users. I checked my Gmail Spam folder as recommended on the forum and found 26 cache found notifications dating back two weeks.
If you haven't been getting the emails lately, and have Gmail, you may want to check the Spam folder. If you check the desired emails and click on Not Spam, they will transfer to your in box and should not be blocked any more.