As a GMail user, one of the techniques to identify who is selling your email address to spammers is to register on their web site using a modified email address. Specifically
It strikes me, that it might be useful to be able to extract the extra identifier and perform rule actions with it. In this case we extract the value “freestuff” and move it into some-identifier.
“if some-identier == freestuff” move message to freestuff folder. Stop.
It is GMail specific, but might be useful to some customers.