If you are an iPhone or Android phone user and want to send emails when you are offline such as in airplanes or in subways, previously you had to wait until you are connected. But now you can compose emails even when offline, Google has added a new option in Gmail that allows you to store emails and send it as soon as the phone is connected the next time.

Gmail has a new “Outbox” option as shown in the figure, by which you can edit emails and store in Outbox. As soon as you are connected to your phone network the next time, Gmail sends the emails in the Outbox.

The Outbox option was still there before but it was hidden from the user, so there was no way to see or edit the emails waiting to be sent. Now, Gmail has made the Outbox option visible and available along with other basic email functions such as inbox, spam, drafts, sent mail etc.,

To solve this problem, we're now introducing a new feature, called Outbox. Outbox is a new label that appears in the menu when you have queued messages stuck on your phone and presents a read-only view of the subject of those messages. So if you want to make sure the previous message was sent before writing a follow-up mail, you can go ahead and find it in Outbox. Please note that you can read only the subject, not the body, of messages in Outbox.

Official Google Mobile Blog: The Iterative Web App: Outbox for Emails in Limbo

You can check this option out by visiting gmail.com in your iPhone or Android phone browser. According to Google blog, this will support only iPhone/iPod Touch OS 2.2.1 or above and will work in all Android-powered phones. It is available for US users only but will soon become available for all users.