Email filters

I have enabled spamassassin on my domain, and some keyword filtering on a particular email address which is both forwarded to a non-DH domain and delivered to the mailbox. As mentioned on the wiki, the forwarded mail doesn’t get filtered. At my previous host, all mail into the domain was passed through spamassassin and tagged appropriately, then passed through my exim filter file in my home directory. I was able to hand edit this filter file so that I could do things like fail junk mail and deliver the rest both local and off-domain. I was curious if anyone has done this with their DH hosted domain, and if so what tips they have from that experience.