A user on the e-mail system is an actual POP3 e-mail account. Mail can be sent to this account and retrieved from this account independent of any other POP3 mail account. Every POP3 account can have many different alias. An alias is simply another name for the existing e-mail account.

As an example, you can create a user called support@yourdomain.com. This user account is a full POP3 e-mail account. Now you can assign multiple alias to the account. Some possibilities might be techsupport, hardwaresupport, softwaresupport and so on. People can now send e-mail to support@yourdomain.com or to any of the alias accounts such as techsupport@yourdomain.com. Regardless of how the mail is addressed, to the user name support or any one of the alias, the mail will be delivered to the support@yourdomain.com mailbox.