Acccesing Gmail in offline mode is quite useful option for me, as it allows to access my Gmail account when I am not connected to the web. To set up – You have to download Google Gears.

It’s a simple process from within Gmail. Head over to your “Settings” menu, hit the “Offline” tab, and check the option to “Enable Offline Mail for this computer.”

Note: Offline Gmail works only on Microsoft Internet Explorer versions 7.0, 8.0 and Mozilla Firefox versions 3.0 to 3.6.

Once you save the changes, Gmail will auto-prompt you through the process and even gives you the option to create a desktop shortcut for quick access to Gmail when offline. Now I can search, read and compose e-mails when you’re not in a Wi-Fi zone, and Gmail will simply auto-update (and send/receive any new mail) when you next reconnect.

Just follow these steps to set up your offline access:

From your inbox, Click the gear icon in the upper-right and select Mail settings at the top of the Gmail page.
Select the ‘Offline’ tab in your Gmail Settings and select the ‘Enable Offline Mail for this computer’ radio button. Adjust any other offline settings on the ‘Offline’ tab before installing Offline. Click Save changes.

You’ll see a prompt from Gears to start downloading your messages onto your computer. If you don’t have Gears installed, Gmail will help you install it (you can also download it here if you have the correct system requirements). You may need to restart your browser1 after installing Gears. If you already have Gears installed (for example, to use Google Docs offline), you won’t need to install it again, but you’ll be prompted to allow permission for Gmail to access Gears. Click the allow link.
Your messages will be downloaded to your computer. Depending on the size of your account, this may take a while the first time, but you can check on your progress in the status box near the Settings link under the Gear icon.

You can use Gmail normally while syncing. You don’t have to wait for synchronization to finish before disconnecting from the internet. If you’d like, you can click the pause sync button to temporarily stop the sync process (it’ll resume automatically if it’s been paused for an hour). When you disconnect from the internet, the messages you’ve synchronized will be available immediately. Gmail will automatically continue syncing in the background whenever you reconnect to the internet.