If you're at an enterprise that's been thinking about transitioning your email infrastructure to a hosted software-as-service model then Goolge's new Apps Email Migration API may be of interest. As you can see in our API profile the Atom-based API is designed to let corporate developers and email administrators do things like selectively move email messages across systems individually or in batches. This can appeal to larger companies that have more complex email and messaging platforms who may need to run systems in parallel or migrate groups or individual accounts over time.
As Google Apps product manager Gabe Cohen announced on their Enterprise Blog:
We're excited to announce the new Google Apps Email Migration API, which can move email from anywhere – not just IMAP systems – to the Premier, Education or Partner Editions of Google Apps. If you need to migrate email from your users' desktops, migrate email from a server not supported by the IMAP migration tool, or do a push migration because of your security policies, a tool built on this API could be the perfect answer...If you're interested in building an email migration tool yourself using this API, you can create an administrator or end user tool to migrate email extracted from any data source. The email migration API is based on GData, so it's easy to use, and you can learn all about it on the Google Code website.
One of the first third-party applications built on this API is gMove, our Mashup of the Day today from LimitNone. gMOVE is a migration utility for moving your Microsoft Outlook calendars, email, contacts and tasks to Google.