The roh dothack, not to be confused with Cyrus dothack, is a method for easily identifying spam mail, as well as making it easy to sort inbound mail.
Implementing the roh dothack is a matter of instructing your MTA to deliver all mail destined to foo.bar@example.org to foo@example.org, regardless of the value of bar. Using rules matching the second field of the destination email address, you can filter mail into a specific IMAP folder, for instance. Or, you can delete the mail because you know it is spam. (On my MTA, mail destined to cartel.real is automatically dropped. Thanks for nothing, RealNetworks.)
In Postfix, this can be implemented using the following PCRE virtual alias map:
/(.*)\.(.*)\@example.org/ $1
Of course, replace example.org with your domain name, and repeat for any other virtual domains you may want to implement the dothack under.
If anyone bothers to implement this under a different MTA, please tell me, and I will write it up here.