An e-mail alias is actually an e-mail that shares a mailbox with a different e-mail. For instance, you could have firstname.lastname@example.org and also email@example.com and emails sent to either one of them will be received in one and the same mailbox. This feature will make it less difficult and more convenient to control a variety of addresses as you will have to log into only one mailbox if you work with webmail or configure just one address in a e-mail application on your computer. When you set up an alias, you will not only have the ability to get e-mails, but you will also be able to send emails from the various addresses and they will share the Outbox, so you will have all communication in one place. Using aliases is a replacement for making use of various mailboxes for different purposes or forwarding a single e-mail address to another one to be able to control the emails of both in a single location.