How to read Gmail offline

Earlier this year, Gmail owned by Google, introduced a feature called Offline Gmail that will allow users to check their mailbox while offline.
The way Offline Gmail works a copy of your mailbox with the latest messages in it, is downloaded while you are online, and then stored on your browser for later viewing offline.
The function needs to be turned on by logging to your Gmail account, click the Settings tab and then the Labs tab. From there, click the Enable button for Offline Gmail and hit the Save Changes button.
Once those steps are taken, you can start downloading your mailbox by clicking the new Offline line on the mailbox page.
Web-based mail is great — until you don’t have an Internet connection. To ease the separation anxiety, Google recently introduced a feature called Offline Gmail, which downloads a copy of your mailbox and all the recent messages when you do have Internet access, and then keeps it all available in your Web browser for when you don’t.
To turn it on, log into your Gmail account on the Web, click the Settings tab and then, in many browsers, the Labs tab. Click the Enable button for Offline Gmail and then the Save Changes button.
To start downloading your mailbox, click the new Offline line on the mailbox page.

For more information, go to the Gmail Blog where a video explain the process in simple terms can be viewed.