External source: http://msexchangeteam.com/archive/2010/08/09/455756.aspx
Have you ever wondered why, in Exchange 2010, you can create a new mailbox and you don't have to tell Exchange in what mailbox database it should be created? Or had an administrator in one department create a mailbox, and the mailbox is created in a database that their department isn't assigned? If you've answered 'yes' to either of those questions, you'll want to check out a new article that was just posted today on MS Exchange blog.
Where Did That New Exchange 2010 Mailbox Go? introduces you to automatic mailbox distribution, which is a new feature added to Exchange 2010. The article talks about how automatic mailbox distribution works, steps you through the selection process, and shows you how you can control it using exclusions, Active Directory sites, and (in Exchange 2010 SP1) database scopes.
Take a look at the article and let us know what you think of this new feature.