In a huge move, Google is rolling out offline support for Gmail users, which means you’ll finally be able to read and write email even when you’re not connected to the web.

Jeez, I’ve been waiting a while for this one. And so have many others.

Even though Gmail adoption has been strong to date, it’s had to play catch up to other popular online-only email services like Hotmail and AOL. In part, it’s growth has been hampered by its inability to work offline.

This move essentially takes the shackles off Gmail, giving it the flexibility to match Microsoft’s flagship email service, Outlook — which lets millions of office workers and consumers check their email both online and offline. The big difference: Gmail is free. This is actually a major attack on Microsoft, because it wipes away one of the biggest technical deficiencies remaining in Gmail.

Yahoo Mail, meanwhile, is the world’s leading online email service. Gmail is just a fraction the size of Yahoo Mail, but this move could give people more incentive to switch.

A company spokesperson says users of Google’s business software package Google Apps will also be able to view their Calendar offline sometime in “the next couple of weeks.”

The changeover has been rumored for a long time. For example, consultant Andrew Fogg reported seeing offline versions of Gmail and Calendar back in July, and said they would be available in six weeks. Obviously that didn’t happen. Perhaps bringing Gmail’s powerful search tool and gigabytes of storage offline proved more complicated than expected. Meanwhile, an hours-long Gmail outage in August illustrated the the dangers of storing data in the internet cloud.

Gmail Offline uses Google’s Gears technology and must be “turned on” via Gmail Labs (where Google tests out new features). It will be available for both consumer Gmail accounts and Google Apps business accounts (in some cases, your Apps domain administrator will need to enable the feature). And as with other Gmail features, the rollout will be gradual and random; if you don’t see it right away, it’ll probably come your way in a day or two.

Of course, you have to wonder how Google balances Gmail’s promise that you’ll never need to delete an email again with the requirements of offline support, which involves downloading emails to your desktop. In my case, that could take up to 3 gigabytes of my hard drive. But Google says Gmail Offline only downloads some of your emails: “A good chunk of the inbox, all starred messages, ones you’re drafting, recent sent mail, etc.”

I haven’t been this excited to try out a new Google product in a long, long time. If Gmail Offline works as promised, I expect I’ll be uninstalling Mozilla’s Thunderbird email client ASAP, since I just use it as a backup for my Gmail account. I also expect many desktop email users to make the (complete) switch to Gmail, since they’ve run out of excuses to avoid it. Matt Marshall, I’m looking at you [Update: Matt’s happy. See comment below].

[photo:flickr/Lance and Erin]

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