Gmail does provide POP3 access so you can easily read your Gmail messages offline in Outlook, Outlook Express, Thunderbird or any other email client. The only problem with the POP3 approach is that Gmail cannot synchronize with Outlook so there’s lot of duplicate work.
For instance, if you download your emails from GMail to Microsoft Outlook and mark them as read, the messages will still show a status of “Unread” in your Gmail Inbox. Similarly, if you delete emails in Outlook, they’ll still exist in your Gmail account.
These limitation of POP3 are a thing of the past has Gmail has added support for IMAP – that means, in very simple terms, if you delete a message in Outlook, it will also be deleted on the Gmail server.
When you Flag a message in Outlook, it’s starred inside Gmail. When you move a message to Outlook Spam folder, it’s equivalent to reporting that message as SPAM in Gmail.
The best part – if you move a message downloaded from Gmail to some Outlook folder, Gmail automatically applies a label to that email on Gmail server with the same name as the Outlook folder.
IMAP support will be a blessing especially for Gmail users who manage multiple web email accounts from Outlook or Windows Live Hotmail. There’s little need for a GMail offline client now.
To use this feature, you will have to enable IMAP through the POP/IMAP and Forwarding settings of your Gmail account. If you don’t see the IMAP settings it in your account yet, wait for some more time.
If you are using Gmail with Google Apps, always enter your full username during the configuration process including your domain.
Remember that IMAP is only for synchronizing your emails. To sync your Outlook contacts with that of GMail, you will still have to export the GMail contacts as an Outlook CSV file (see example) and import that into Outlook.
Update: The official announcement is up the Gmail blog.