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The primary SA documentation at http://wwwspamassassin.spamassassinapache.org/full/3.1.x/dist/doc/Mail_SpamAssassin_Conf.html#scoring%20optionshtml#scoring_options defines the required_hits parameter, and states,
5.0 is the default setting, and is quite aggressive; it would be suitable for a single-user setup, but if you're an ISP installing SpamAssassin, you should probably set the default to be more conservative, like 8.0 or 10.0.
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