Gmail works via POP3 using a system of access flagging. Once a message is flagged as having been accessed once, the default is to not download it on subsequent POP accesses. The POP flags can be reset by going to your Gmail account online and changing the POP access settings. A copy of the mail is downloaded to your mobile device but the mail is retained in the server-based mailbox. The effective result is that the device mailbox is emptied on each mail check and only new mail is downloaded. If you want to keep a complete copy of your Gmail inbox on your device, you need to change the default behavior through one of the suggested changes.
If you only want to keep selected mail in your device inbox, I have found the method that works best for me is to create a non-syncing subfolder in the devc=ice inbox account named Saved or something similar and then copying the desired messages into that subfolder. You can still forward and reply to messages in that subfolder but it does not require changing the main folder's default action to retain only new messages on each mail check.
I have moved to nPOPuk as my default email client because it retains some of the threading that is used in the online Gmail client. It isn't a perfect threading system, but does work when the messages are requential in order.
The flag system means that to remove messages from the server, you need to actually delete them, either through the web site or by doing a delete command in the email client. While Gmail uses POP, the flagging gives it some of the behavior of IMAP rather than standard POP.  |