This was happening to me on my yahoo account. All of the sudden id get 30 emails after i turned on and unlocked my phone...all from the past few days that I had deleted. I thought it may be due to the turning off of data after x minutes in the battery settings and since ive changed that to always on, i havent had the issue, although it has only been a few days. It never did it to my aol or gmail but I dont get emails on them as much as yahoo.