Google took a giant step on Friday to make it easier for companies to migrate any e-mail system over to Google Apps Gmail by offering an E-mail Migration API targeted at corporate developers and e-mail administrators.

"We've provided developer documentation and sample code that allows developers to build extremely sophisticated mail migration tools, some of which can be run by administrators to migrate centralized mail and some of which can be run by end-users to migrate mail from the desktop," said Gabe Cohen, Google Apps product manager.

Previously, Google released an IMAP migration tool that allowed end-users and administrators to migrate from most IMAP-based e-mail systems to Google Gmail.

The new migration tool will move e-mail from any system, including Microsoft Outlook calendars, e-mail, and contacts into Google Apps, or any other type of mail server to Premier, Education, or Partner editions of Google Apps.

"Migration is a difficult problem with many edge cases," said Cohen, adding that Google has now exposed enough functionality that, in theory, any migration scenario into Google Apps is possible.

In releasing the new API, Google appears to understand that any mid- or large-sized company would be reluctant to rip and replace its current e-mail server with another system. However, by allowing a company to run both systems concurrently, Google may have ameliorated a major concern.

Companies like Capgemini, with 80,000 employees are in fact putting a first toe in the water and using Google Apps for some of its employees.

Google Apps E-mail Migration API is available now.