This article will show you how to change the email address for your Hosted Exchange mailbox.
Sometimes you may wish to set a different “From” email address to the default address for a mailbox. It may be that you want replies to go to a different address, or you want to change the primary email address associated with a mailbox (effectively renaming that mailbox).
If you wish to set the primary email address to one that is already associated with that mailbox (i.e. an alias) select E-mail address and click Next.
If you wish to choose a custom e-mail address (e.g. one not associated with your domain or this mailbox) select Custom e-mail address and click Next.