Google Gmail engineer Chad Perry likens switching e-mail providers to leaving a relationship.

"You have so much baggage -- years of e-mails and contacts, memories of past Christmases and Valentine's Days -- so the easier your new e-mail account can make it, the better," he explains in a blog post.

In keeping with Perry's breakup metaphor, Google plays the role of the home-wrecker, seducing frustrated users of Microsoft Hotmail, Yahoo Mail, AOL, and other services to give fresh-faced Gmail a go.

On Wednesday, Google introduced a new migration tool to make it easier to export e-mail messages and contacts from competing e-mail services. The tool is available in all newly created Gmail accounts and is being rolled out to older ones over the next few days. It supports e-mail extraction from more than 40 different e-mail providers.

It's not available to businesses and schools using Gmail through Google Apps accounts.

Google's dance of seduction appears to be turning some heads. Gmail's growth rate in the United States last year was significantly higher than the growth rates of its major competitors.

Between December 2007 and December 2008, Gmail's number of unique monthly visitors in the United States rose from 20.8 million to 29.6 million, according to ComScore, a 43% increase. During this period, Windows Live Hotmail saw its number of unique monthly visitors drop from 46.2 million to 44.6 million, a 5% decrease. In December 2008, Yahoo entertained 91.9 million unique monthly visitors, up 11%.

Based on those trends, the number of Gmail users in the United States could surpass the number of Hotmail users in the United States by the end of 2009, and could surpass the number of Yahoo Mail users in the United States in late 2011 or 2012. But presumably both Microsoft and Yahoo are taking steps to prevent this future from coming to pass.

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