Using the following method, any email that goes to user@domain.com, and if that user does not exist in the Kerio server, the mail will be caught and forwarded to a specific mailbox within your domain.
1. Create a mailbox for this purpose.
2. Create an alias such as: * –> mailbox from above step. (so * –> mailbox)
Any mail coming into the domain, if no user is found, the email will be forwarded to this account.
http://www.maccius.com/