Microsoft introduces online tool for Gmail switchers
The service allows you to set up an Outlook.com account, connect it to an existing Gmail account using the secure OAuth protocol, then copy existing messages from Gmail to Outlook.com. gmail-switcher1
The automated setup process works in the background, on Microsoft's servers, and it's smart enough to migrate new messages first and maintain the read/unread status for anything in your inbox or in folders.
The final step is the only one that requires manual intervention, with the user following Microsoft’s instructions to set up auto-forwarding of new messages sent to the Gmail account.