The Dreamhost junk filter sucks. If you're a bit comfortable with the command line, I strongly recommend you to disable it and install your own Spamassassin. It's not really hard, and it gives you the option to train it on known spam (Bayesian filter), filter out specific languages/scripts etc.
Instructions: Spamassassin for Dreamhost
Make sure to whitelist all addresses in your addressbook. Don't whitelist your own email address or domain, recently a lot of spam uses that. Don't touch the junk or folder filter settings in squirrelmail after installing your own Spamassassin!
I've set up two folders, Spam (or Junk for compatibility with some mail clients) and Ham, that is ~/Maildir/.Spam and ~/Maildir/.Ham . When some spam slips through, I move it to Spam, all legit mail I copy to Ham. After an initial training phase, it's sufficient to just copy false positives to Ham. The Bayesian learning script runs as a cron job every night and empties these folders. (There could be a problem with learning from false positives, so maybe there should be a third folder where Spamassassin moves recognized spam.)
It works remarkably well for me after training it on a few dozen spam and ham mails - about 1% false negatives, no false positives in 2 weeks.