I tend to play in fits and starts.. rather than keep turning on and off the email alerts it would be nice if I only received them if I hadn't moved within X hours/days.
Then if I'm playing multiple moves on multiple games within a short period of time I don't get mail - and don't need it, since I'm aware of the moves made from the games waiting etc. I'd then get only one mail for the last moves I hadn't responded too, if there were any.
..not that I mind much with a filter on my mail but if I don't delete them I wonder then when they arrived.. was it while I was playing, or since then?