Your Exchange account comes with a pre-installed domain that looks like accountname.serverdata.net. It is a free domain name that we provide for you as a courtesy in case you do not have your own domain name. Mail Exchanger (MX) records of this domain point to Exchange.
Each mailbox on your account will automatically have an alias set up for the accountname.serverdata.net domain name. You can start receiving email to your Exchange mailboxes using those email addresses.
If you already own a domain name purchased through a registrar, read the Knowledge Base article on How do I start receiving email on Exchange with my own domain name? for instructions on setting this up.