Hi -
This is the TCH installed Squirrelmail. In Squirrelmail, if you goto options, towards the bottom on the left hand column, is "SPAM Filters". The particular DNS filter I was trying to enable was the Spamcop filter.
I should also say, that I'm accessing squirrelmail by the following url: www.congdon.ws/sqmail . This appears to be a different install of squirrelmail than www.congdon.ws/webmail .