iPhone pulls in old mail

I noticed after the 3.1.2 update when I check mail on my iPhone it pulls in old mail that I've already opened & looked at on my iMac. It didn't do this previous. Normally it would only pick up mail that I haven't opened. I'm not running any type of Mobile ME or anything fancy, just POP3 from my mail account & that's it.

Any suggestions on why old mail keeps popping up. I'm talking about stuff from last week still gets pulled through.

PS (Sorry I forgot to add I have the 3G)

I also had that problem for a while then it mysteriously went away without me changing
anything. Also do you send old mail to trash ?

Sounds like a setting on your email client on your iMac needs to be changed. Not sure what email client you are using. In Entourage there is a setting to leave read emails on server. If this box is checked, you'll receive duplicate emails on different machines. Typically, you should be set up so that POP3 emails are removed from the server once they are received by your primary email machine. Whatever secondary device you are using to also view your emails (your iPhone) should be set to leave messages on the server.

Also, the 3.1.2 update was released several months ago. Perhaps you are referring to the 3.1.3 update?