I'm not sure why, I did a quick search and didn't see anything similar, but my SGS3 is re-notifying me on emails I've already read. The only way that I can stop the notification, so far, is to delete the email. Lucky they've been rather unimportant emails (airmiles, dropbox) so it hasn't been a huge issue, but it's this side of annoying. I have 2 Gmail accounts synced, and am running my phone stock out of the box. Is there some setting that I'm missing?