How do I use router-filter (to block MSN subscription requests)?

I'm using Jabberd2 v2.2.8 on Ubuntu Server 10.04. I'm the only user.

I'm getting a lot of subscription requests from MSN. They are spam (or spim?). I want to block them. I found the router-filter.xml file. It looks ideal for this purpose.

This is my current attempt at a rule to block MSN subscription requests:

<rule from="*%hotmail.com[at]msn.my.domain.tld" to="*" what="subscription='none'" error="not-acceptable" log="yes"/>

(Please replace "[at]" in the above with the actual "at" symbol. Launchpad seems to scrub it.)

I don't really know what goes in 'what', beyond an "XPath like query". I don't know what the 'error' should be either: "not-acceptable", "forbidden", or something else?

Can someone direct me to some documentation explaining router-filter or modify my rule?

Thanks for any help.