SAN FRANCISCO - Google Inc.'s free e-mail service will shed the final remnants of its invitation-only restrictions Wednesday, extending the reach of an increasingly popular product that has emerged as a vital cog in the online search leader's expansion efforts.
Invitations will no longer be required to join the nearly 3-year-old "Gmail" service in the United States, Canada, Mexico and a swath of Asian and South American countries where the Mountain View-based company previously limited the number of users.
With those restrictions now lifted, Gmail will be open to all comers worldwide for the first time since Google unveiled the service on April Fool's Day in 2004.
"It's a pretty momentous time for Gmail," said Keith Coleman, Google's product manager for the service.
Although it will no longer require invitations to sign up, Gmail is retaining its "beta," or test, status, signaling that Google still considers the service to be a work in progress.
Making Gmail more widely available is important to Google because other key products like instant messaging and calendar management are tied into the e-mail service, company co-founder Sergey Brin said an interview. "It has become a real cornerstone for us."
Because Gmail users often remain logged into Google's Web site while they conduct online searches, the service also helps the company's engineers learn more about individual preferences , knowledge that can help deliver more relevant search results and foster more loyalty.
The decision to lift all invitation requirements on Gmail signals Google finally believes it has adequate computing capacity to accommodate the generous amount of free storage provided by the e-mail service after investing heavily in additional data centers. Gmail offers each account at least 2.8 gigabytes of storage , enough to fill about 1.4 million pages.
In 2006 alone, Google's capital expenditures totaled $1.9 billion, with much of the money going toward additional computing capacity. It's an investment that Google could easily afford, having earned $3.1 billion on revenue of $10.6 billion last year.
Now that Google has more computing muscle, Brin said the company will start selling additional storage capacity to e-mail users with extraordinary needs. Google still hasn't figured out the specifics, but Brin indicated the e-mail storage and fees to be introduced later this year would be similar to Google's photo-hosting service that charges $25 annually for 6.25 gigabytes and $500 annually for 250 gigabytes.
"We can't afford to give away everything for free," Brin said.
Google tries to make money off its e-mail service by electronically scanning the content of the communications so it can display advertising links tied to the topics being discussed.
Gmail's advertising methods have raised some privacy concerns and turned off some potential users who don't like the idea of their e-mail discussions being perused or commercialized.
Nevertheless, Gmail has been growing rapidly as Google gradually opened the service in other parts of the world and made it increasingly easy to wrangle an invitation where the restrictions were still in effect.
Like the other major providers of free e-mail, Google won't specify how many users it has. But statistics compiled by the research firm comScore Inc. indicate Google has surpassed AOL to become the world's third largest e-mail service behind longtime leaders Yahoo Inc. and Microsoft Corp.
In December, Gmail attracted 60 million unique visitors, a 71 percent increase from the prior year, according to comScore Networks Inc.'s World Metrix. Despite that progress, Gmail remains far behind Yahoo Inc.'s free e-mail, which increased 11 percent to 249 million unique visitors and Microsoft's Windows Live Hotmail, which rose 13 percent to 236 million, comScore said.
Representatives for Yahoo and Microsoft, which don't require invitations, declined to comment specifically on the broader access to Gmail.
Google seems unlikely to catch Yahoo's and Microsoft's competing e-mail services any time soon, particularly since so many people are reluctant to change their existing addresses. But Gmail still "should gain some serious traction this year," predicted Jack Flanagan, a comScore analyst who follows the e-mail market.
Brin said he doesn't especially care if Gmail ever becomes the largest e-mail service. "The trick isn't getting more people to use the service. The trick is to get more people to use the service more effectively."
Even though Gmail hasn't been universally available, its existence already has affected just about anyone with a free e-mail account by pressuring the market leaders to dramatically increase the storage capacity of individual mailboxes.
Sunnyvale-based Yahoo now provides 1 gigabyte of free e-mail storage while Redmond, Wash.-based Microsoft offers 2 gigabytes per e-mail account. "We will continue to listen to Yahoo users worldwide to evaluate our storage offering and to make sure our users always have as much as they need," Yahoo spokeswoman Karen Mahon said.
Both Yahoo and Microsoft were giving away less than 10 megabytes of e-mail storage when Gmail launched.
"We have already made e-mail better for everyone in the world," Google's Coleman boasted.
Since Gmail's arrival, both Yahoo and Microsoft have introduced upgraded versions of their free e-mail services that also remain in the beta phase. In another move that mimicked Gmail, Yahoo this week introduced a feature that allows instant messaging chats to be conducted within its e-mail service.