When you create a user, by default that user has email addresses of <username>@<domains>.
o<username> is the user account name.
o<domains> for incoming messages from a catch-all account is the list of domains in theAccepted domains setting.
o<domains> for locally sent messages or incoming SMTP messages is the list of domains in the Local domains setting.
For incoming mail from individual ISP mailboxes, the email address is set at the ISP, not within VPOP3.
In most installations, these defaults make it easy to manage email addresses. You can add extra email addresses to an account if you wish.