Creating an email alias means making an e-mail address that shares the exact same mailbox as a completely different e-mail address both for the inbound as well as the outbound emails. For example, you can create an e-mail address email@example.com and it'll be linked to its own mailbox. Then, you can make an alias firstname.lastname@example.org, that will use the mailbox of sales@ and does not have a mailbox of its own. Once you look at your email messages, you'll see messages sent to both of the two addresses in a single place, which might be more convenient in some instances since you will not have to log in and out of various email addresses working with webmail or set up many email addresses in an email program. This option is normally used as an alternative to forwarding e-mail messages from a single address to another one if a number of email addresses are mentioned for contact on a site.