The offline support is made possible by Google Gears, which you’ll need to download in order to utilize the feature. Here’s how it works, according to Google’s Andy Palay: “When you lose your connection, Gmail automatically switches to offline mode, and uses the data stored on your computer's hard drive instead of the information sent across the network. You can read messages, star and label them, and do all of the things you're used to doing while reading your webmail online.”
Once you’ve re-established a connection, the messages you send while offline will be delivered. There’s also a "flaky connection mode" for times when your connection is weak, but communication with Gmail is still possible. Like Gmail’s other experimental features, offline mail is currently available via Labs, which can be found under the “Settings” tab.
Between PDAs, WiFi on planes, and broadband cards, situations where you don’t have Internet access might be far and few between these days, but if you have a never-ending stream of email flowing into your Gmail, offline mode should help you keep up even when you can’t find a way to get online.
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