spam getting through

[mist_firefly]

We have a client that keeps getting lots and lots of spam.

What we are currently using is spamdyke and spam assassin but things still get through to him.
We noticed some similar addresses in the spam emails and I would like to try to create a rule with those exact words in but I don't know how. the words are
18_Parkway_Court Brooklyn_ny_11223

Also please point me in the right direction of what I should do for this specific client only, to stop all this spam going through to his inbox. (different rules only for his domain? how? )

Thanks