IMail has a unique feature called a Nobody Alias.
The is a catch-all alias which receives messages from users that do not exist on your IMail server hosts, and forwards the message to the address specified in the "nobody" alias.
To create a "nobody" alias simply to the domain you want to use it, giving standard alias name of "nobody". In the "Resolves To:" box add the email address(s) of the user(s) you want all of the email to go to.
To send all email from the Nobody alias to the postmaster account, put Postmaster in the Resolves To: box of the Nobody Alias.
To DELETE all email that the Nobody alias collects, put root-NUL in the Resolves To: box of the Nobody alias.
Warning: Using the nobody alias can increase the amount of traffic to your server. Spammers will think that you are 1. an open relay, or 2. they are sending to legitimate addresses on your server. Use with caution!