Out of the box, SpamAssaassin is not especially great at
detecting what is spam, and what is ham (legitimate email). In order to
drastically increase the detection levels, you must first collect email
and sort it into spam and ham, with the bigger the collection the
better. After this is done, in ssh you can run the sa-learn command to
train spamassassin. The format of this command would be:



sa-learn —showdots —(ham or spam) —mbox -u username —sync /path/to/filename



Note: if you have a Maildir setup, then do not use the —mbox flag



After this, you can monitor your spamassassin log to see if the detection rates have gone up.