An e-mail alias is an email address that shares a mailbox with a totally different email. For example, you can have firstname.lastname@example.org and email@example.com and emails sent to either one of them will be received in one mailbox. This feature will make it less difficult and much more convenient to control various e-mail addresses as you will have to log in only one mailbox if you use webmail or set up one single e-mail address in an e-mail client on your PC. If you set up an alias, not only will you be able to get emails, but you'll also be able to send messages from the various addresses and they'll share the Outbox, so you'll still have all communication in a single place. Using aliases is surely a replacement for using different e-mail addresses for a variety of purposes or forwarding one address to another one so that you can manage the communication of both in a single place.