Catch-all or wildcard email forwarding simply forwards all destination addresses within a given domain to any other email address.
Any other individual email maps within your domain will work as expected, and if a catch-all map is defined then anything else will be forwarded as per the catch-all map.
As with other mail maps, you can also forward to multiple addresses.
This is handy for setting up “email canaries” where you use a distinct email address for each one of your online vendors or membership sites:
twitter @ markjr .org
This way if you start receiving spam or worse you can tell which vendor allowed your email address to leak, either by selling your contact info or from suffering a data breach.
You can shut down a specific email that is getting a lot of spam by using the special mailmap: DISCARD
myspace @ markjr.org -> DISCARD
Be aware that when you enable wildcard email you will get additional spam from simple dictionary attacks that spam bots are known to undertake