GMAIL Blog :”Today we’re starting to roll out an experimental feature in Gmail Labs
that should help fill in those gaps: offline Gmail. So even if you’re
offline, you can open your web browser, go to gmail.com, and get to
your mail just like you’re used to.

Once you turn on this feature, Gmail uses Gears
to download a local cache of your mail. As long as you’re connected to
the network, that cache is synchronized with Gmail’s servers. 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. Any messages you send while offline will be placed
in your outbox and automatically sent the next time Gmail detects a
connection. And if you’re on an unreliable or slow connection (like
when you’re “borrowing” your neighbor’s wireless), you can choose to
use “flaky connection mode,” which is somewhere in between: it uses the
local cache as if you were disconnected, but still synchronizes your
mail with the server in the background. Our goal is to provide nearly
the same browser-based Gmail experience whether you’re using the data
cached on your computer or talking directly to the server.”

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