Emails deleted on mobile device

[twentw]

I've set up my phone (TMobile MDA) to get email from a Gmail account (by accessing Gmail POP server, not forwarding). The phone appears to download the email fine on the first send and receive, but the next send and receive deletes the email downloaded previously. People on the TMobile forum say this is a Gmail problem. In Gmail, there are two settings "Enable POP for all mail (even mail that's already been downloaded)" and "Enable POP only for mail that arrives from now on." It doesn't make any difference which of these I choose, the mail always gets deleted on the subsequent send and receive.

Anyone know what's going on? Thanks.