I could not find any help in what I have experienced. Though, search terms that limited results were tough to come by.
Anyhow, I used to get all my emails, on my BB before even my desk top. Now, some seem to be immediate (not just within 2 minutes) some are 7-15 minutes late, and some are an hour or so late.
I have an 8130 with Bell. I use Gmail for email, and did all the steps when I first got the phone to have push email and not duplicated sent messages, etc...
I installed 2 apps around when this was happening, and have since deleted them hoping this would help. One was BillTracker (or something like that) and the other was Buddy Guard.
