[frejos]

Actually, you can tell the IMAP to not delete it from the server as well. It's in the options when you set up the account on the device just like it is in the POP3 configuration.

IMAP is a folder aware protocol, it will maintain folder structures, and synchronizes the folders. If you read, move, delete an item on the device it does the same thing on the original copy. (Except if you tell it not to delete from the server when you delete from the device.)

POP3 downloads one folder your inbox and either removes it from the server when it downloads it or leaves it. No other synchronization takes place.

As far as I know gmail is the only big free provider that supports IMAP, although it is a common protocol. IMAP is also common with exchange and outlook servers.

-Josh