On Tuesday, Google said it plans to make offline functionality for Gmail available through the Gmail Labs Settings tab.
Once enabled, a new "Offline" link will appear in the upper-right-hand corner of the user's Gmail browser window. After clicking on that link, most or all of the user's Gmail messages, depending on the size of the mailbox, will be synchronized to a local cache. Thereafter, those messages will be readable offline. Gmail users also will be able to compose and save new messages that will be sent when Internet connectivity is available.
As is typical with new Google services, not every Gmail user will have access to this option immediately. It may take a day or more before the Gmail change propagates across Google's infrastructure.
In the next few weeks, Google Apps users also will have offline access to Google Calendar, with general availability coming later.
The offline version of Calendar will be read-only, at least initially, meaning that changes cannot be made offline for subsequent online synchronization. Users of Google Apps Standard Edition will be able to enable offline Calendar use when it becomes available. Google Apps Premiere Edition and Education Edition users will have to have the option enabled by their Google Apps administrator.
Rumors about the availability of offline Gmail access have been circulating for months. In July last year, several Google bloggers said they expected that Gmail and Calendar would work offline using Gears within six weeks. It turns out that the coding work was rather complicated.
"Gmail offline was probably one of the toughest tasks that we've had, just through the sheer volume of information that people typically get with e-mail," said Rajen Sheth, senior product manager for Google Apps.
Sheth said that Gmail users with massive mailboxes may not be able to access all of their e-mail. Gears copies the most recent messages for offline availability, based on an algorithm that determines how much mail can be stored without affecting system performance.
However, Gmail users have some control over what gets replicated offline. All messages in the Starred Folder, for example, will be copied to the local cache, making it possible to designate messages for offline use. Sheth said that his in-box contains thousands of messages and that he has had offline access to all the e-mail he needs.
Google isn't the first to link the cloud and the desktop. Last July, Yahoo released its Yahoo Zimbra Desktop, a downloadable e-mail clients application for Windows, Macintosh, and Linux.
But Sheth said Google is the first major e-mail service to offer offline access through a Web browser. Though there are other technologies that accomplish what Gears does, Sheth contends that the Gears experience is the most seamless.
When Google launched Gears in May 2007, the idea of taking online applications offline looked revolutionary because it foretold a threat to Microsoft's hold on the desktop. Today, with Microsoft among those building bridges between the desktop and the cloud, Gears looks less likely to overthrow the old order.
Other Gears-enabled Web applications include Google Docs and Google Reader, along with several third-party apps like Opera, Zoho Writer, MySpace Mail, and WordPress.