JayBarcelo.com

For the past few years, we’ve offered POP access, which is similar to IMAP but lacks one critical feature: your changes made on other devices aren’t seen in Gmail when you log back in. Instead you are presented with a list of unread mail, and you must re-read and re-sort everything. For this reason, as soon as I started at Google, IMAP was one of the first things I asked about. Since then, I’ve seen countless blog posts, requests, chats, and just about everything else asking, “Are you guys ever going to do IMAP?” Well now I can say: Yes. Yes, we are doing IMAP. In fact, we are doing it for you for free on all devices and platforms.

http://gmailblog.blogspot.com/2007/10/sync-your-inbox-across-devices-with.html