Also available are some other links that should help:http://www.akadia.com/services/postfix_spamassassin.html.
There is some broad information about SpamAssassin, dspam and ClamAV at:https://searchsap.techtarget.com/tip/Eliminating-spam-with-SpamAssassin-DSPAM-and-ClamAV.
And, of course, Google is always your friend. A quick search for Postfix, SpamAssassin and dspam will turn up a number of results.
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