I'd suggest sending the quarantined queue through Spamassassin to separate it into things that you want to look for and things that you don't. First of all that will manage to get most of the legal documents extracted from the mess. Secondly you can improve the review of the rest by adding rules that specifically locate legal-type emails to improve your accuracy.

Of course after a little time with this exercise, you might wonder what value TrendMicros InterScan is adding. But don't ask those questions too loudly. Because your manager wouldn't look good if you did that...