[Darkjedi]

switch to POP3 server protocols. POP3 sends a copy of the mail to your phone and is independent of your mail server. Just make sure that if you're using like G-mail or whatever, you have to make sure it retains a copy of the message on their server, otherwise you're phone will be the only one with a copy.

If you're using IMAP, what you can do is create a new folder within Gmail like Archive or wahtever. Whenever you want to 'delete' the mail you can move it to that folder and it'll disappear from your phone provided that you don't sync that folder. It'll update on your Gmail as under the archive folder though.