An email alias is an email address that uses exactly the same mailbox as the initial e-mail. For example, you could have firstname.lastname@example.org as your authentic email address and add an alias email@example.com. Each of the email addresses can share exactly the same mailbox, so messages sent to either one of them shall be received in one place. You can use aliases for various needs, like emailing different types of people or enrolling on web sites. Any time you begin to get a number of spam, for example, you can easily remove the alias while your actual mailbox will not be changed by any means and you'll maintain the communication that you need. Aliases in many cases are viewed as a replacement for forwarding e-mails from one mailbox to another if you use a couple of addresses for contact on your site.