Deleted e-mail keeps coming back after iOS4 update

I updated my wife's iPod Touch to iOS4 the other day and it ended up downloading 378 messages that were still on the Comcast server, but she had previously deleted off the iPod. We deleted the unwanted messages (approximately 370 of them) but they keep coming back. I went in and manually removed them from the server (supposedly) from her Mail account on OS X but that hasn't helped. Every time we get rid of them they download again. Anyone have any ideas?