Google have just announced offline support for Gmail. Yes it is still an ‘experimental’ feature via google labs, yes you need to have Google Gears installed and yes it is only available via U.S./U.K. English versions of Gmail – nevertheless, this is great news.
Using Google Gear’s functionality, Gmail syncs the cache with Gmail servers when you are online and when you are off, it uses local files to allow you to use Gmail as normal.
When offline, you can read, star, label and even send messages! The message is placed into your outbox and sent once you have internet access again.
If you don’t currently see it available via your Google Labs option in Gmail (go to settings) then sit tight, you should have it enabled over the next few days.