Making an email alias means setting up an email that shares the same mailbox as a totally different address both for the inbound as well as the outgoing messages. For instance, you are able to make an email address email@example.com and it'll be linked to its very own mailbox. Next, you can make an alias firstname.lastname@example.org, that will use the mailbox of sales@ and will not use a mailbox of its own. If you check your emails, you will notice e-mail messages sent to both of the two addresses in one place, which can be far more convenient in some circumstances as you will not have to sign in and out of various email addresses working with webmail or set up multiple email addresses in an email program. This option is often used as a substitute for forwarding emails from a single address to a new one if a number of addresses are included for contact on a site.