Making an e-mail alias means setting up an email which shares the same mailbox as a different e-mail address for both the inbound as well as the outbound email messages. For example, you are able to make an address firstname.lastname@example.org and it'll be connected to its own mailbox. Then, you can make an alias email@example.com, which will make use of the mailbox of sales@ and will not use a mailbox of its own. When you check your e-mails, you will see messages sent to both of the two email addresses in a single place, which may be far more convenient in some instances because you will not have to sign in and out of different mailboxes using webmail or create many email addresses in an email app. This option is commonly used as a replacement for forwarding email messages from a single e-mail address to a different one if multiple email addresses are included for contact on a website.