Google has started offering an API to make it easier for companies to migrate their email to Google Apps Gmail.

"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 centralised mail and some of which can be run by end-users to migrate mail from the desktop," said Gabe Cohen, Google Apps product manager.

Google last month released an IMAP migration tool that allowed end-users and administrators to migrate from most IMAP-based email systems to Gmail.

The new E-mail Migration API will move email from any system, including Microsoft Outlook calendars, email, 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 email server with another system. By allowing a company to run both systems concurrently, Google may have ameliorated a major concern.