IMAP for GMAIL…..unofficial 
Gmail service is great but it does not offer IMAP.
IMAP stands for Internet Message Access Protocol. It is a method of accessing electronic mail or bulletin board messages that are kept on a (possibly shared) mail server. In other words, it permits a “client” email program to access remote message stores as if they were local. For example, email stored on an IMAP server can be manipulated from a desktop computer at home, a workstation at the office, and a notebook computer while traveling, without the need to transfer messages or files back and forth between these computers.
IMAP’s ability to access messages (both new and saved) from more than one computer has become extremely important as reliance on electronic messaging and use of multiple computers increase, but this functionality cannot be taken for granted: the widely used Post Office Protocol (POP) works best when one has only a single computer, since it was designed to support “offline” message access, wherein messages are downloaded and then deleted from the mail server. This mode of access is not compatible with access from multiple computers since it tends to sprinkle messages across all of the computers used for mail access. Thus, unless all of those machines share a common file system, the offline mode of access that POP was designed to support effectively ties the user to one computer for message storage and manipulation.
Key goals for IMAP include:
Be fully compatible with Internet messaging standards, e.g. MIME.
Allow message access and management from more than one computer.
Allow access without reliance on less efficient file access protocols.
Provide support for “online”, “offline”, and “disconnected” access modes *
Support for concurrent access to shared mailboxes
Client software needs no knowledge about the server’s file store format.The folk at Gmail have yet to provide an IMAP interface to their email service. While POP access is nice, there is no folder support and the messages are stateless (cannot be marked read, unread, important, etc.). iGmail is an IMAP server that runs between you and Gmail. You can use any IMAP client (outlook, outlook express, thunderbird, etc.) to connect to your gateway. iGmail is open source, and has been released under the GNU GPL v2.
What does work
All of your labels show up as folders. When you delete a message in your client, it is placed in your trash on Gmail. When you flag a message in your client, it is starred on Gmail. When you mark a message read/unread, that state information is replicated on Gmail. When you get new mail, your filters on Gmail will label your message as you requested (this may include skipping your inbox). You can create new folders (within your labels folder) which will create new labels on Gmail. You can also delete and rename these labels/folders. Generally, what you seen in your client (read/unread/flagged/etc) will be the same as what you see when you log into Gmail.What sort of works
You can copy/move messages between folders that are based on labels, but not to/from your inbox, trash, starred folder, or sent folder. Because Gmail uses “threads” rather than “messages” for read/unread state, you cannot have separate read/unread states for messages. If you mark a message “unread”, the entire thread will be marked “unread”, which means that in your client all other message from that thread will show up as “unread”.What does not work
You cannot delete messages from your trash folder. To permanently delete messages, you will need to log into Gmail.Source and Download: http://www.butterfat.net/igmail/
Update: Gmail now offers IMAP so this is obsolete.
