As counter-intuitive as it may sound, Google — and legions of mobile mail users — are excited about a new feature being tested by GMail Labs: offline e-mail.

Offline GMail doesn’t let you send or receive mail when you can’t get an Internet connection, of course. But it does let you work with downloaded mail until you can connect again.

This is seen as a boon to mobile users who often experience intermittent wireless service — or none at all — while traveling by plane, train or other modes of public transportation.

When you enable Offline, GMail creates a local (on your computer or mobile device) cache of your e-mail messages. You can read messages, compose replies and perform searches in your cache. You just can’t send messages or check for new ones.

When you do establish an Internet connection again, GMail sends any replies or new messages you have composed while offline and updates your cache with any new messages that are waiting on its server.

The official GMail Labs announcement cautions, “Offline GMail is still an early experimental feature, so don’t be surprised if you run into some kinks that haven’t been completely ironed out yet.”

To try Offline GMail, just follow the instructions at the end of the announcement.