http://mail.google.com/support/bin/answer.py?answer=47948
How should I use POP on multiple clients or mobile devices?
If you're accessing your Gmail using POP from multiple clients, Gmail's recent mode makes sure
that all messages are made available to each client, rather than only to the first client to
access new mail.
Recent mode fetches the last 30 days of mail, regardless of whether it's been sent to another
POP client already.
In your POP client, replace '(e-mail address removed)' in the Username field your POP client settings
with 'recent:
[email protected]'. Blackberry users will be signed in to recent mode
automatically, without adding 'recent:'.
Once you enable recent mode, please be sure to configure your POP client to leave messages on
the server according to the instructions below:
In Outlook, on the Advanced tab, check the box next to Leave a copy of messages on the server.
In Outlook Express, on the Advanced tab, check the box next to Leave a copy of messages on
server.
In Apple Mail, on the Advanced tab, remove the check next to Remove copy from server after
retrieving a message.
In Thunderbird, on the Server Settings tab, check the box next to Leave messages on server.