While some companies filter against this, most email services support plus addressing to accomplish the same thing. You can register under myemail+foobar.com@gmail.com, for instance, and all emails will still be delivered to myemail@gmail.com
This is very common, so lots of spammers will just drop the plus-part with a regex. Many sites even prevent signing up with an address containing a plus.
Not trying to tell you to stop though, this is definitely a good idea, when it works.
