My domain provider does:
http://www.tamba.co.uk/
I rely on it as part of my anti-spam measures. I run my own mail server and it just sucks everything down from the one postbox hosted by Tamba then filters/resdistributes internally. Incidently I don't know if this is what you're planning but it's a great way to reduce-heck, eliminate-spam.
I give everyone their own address for me (ie;something.thinkbroadband@mydomain). That way I can:
* Reliabily determine the source of the spam - they can fake most of the header but not 'To'

* Block offenders without impacting anything else.
I've been using this system for nearly ten years now and almost never get any spam. The only time I do I block the offender, optionally notify them, optionally notify their ISP/mail host.
If your email server supports wildcards (and all the good ones do) then adding new addresses takes no effort. Just set up a final rule of "something.*" goes to "something".
Andrue Cope
[Brackley, UK]