An email alias is actually an email that shares a mailbox with a different e-mail. For instance, you could have firstname.lastname@example.org as well as email@example.com and messages sent to both of them will be received in one and the same mailbox. This feature will make it easier and much more convenient to control many e-mail addresses as you will have to log in only one mailbox if you use webmail as well as create only one e-mail address in an e-mail app on your computer. If you set up an alias, you will not only be able to receive e-mails, but you'll also be able to send emails from the various addresses and they'll share the Outbox, so you will still have all communication in one place. Using aliases is a substitute for working with different e-mail addresses for different purposes or forwarding a single e-mail address to another to be able to handle the e-mails of both in a single place.