Email accounts stored on the iPhone can exhibit a number of strange issues including:
- Refusal to accept incoming mail
- Problems retrieving new mail, with the "Last updated" status message showing an old time
In many cases, the fix for these issues is drop-dead simple: delete and re-establish the afflicted account. Tap Settings and then tap Mail. Tap on the problematic acount, then scroll to the bottom and select Delete Account. Go back to the main Mail settings pane and tap Add Account to re-create the account, re-entering your settings. Note that you'll lose any mail downloaded to the iPhone from non-mirrored POP accounts.
We're not sure why exactly mail accounts start exhibiting these issues, or why deleting then re-establishing them alleviates the problems.