The default value (root@localhost) for report_contact in /usr/share/spamassassin/10_misc.cf is rather useless: from #spamassassin <quinlan> root@localhost is not the default (I hope), some package did that <quinlan> it's definitely a bug in the package to set that to root@localhost <quinlan> the actual default is better
This will be fixed in the ebuild for SA 3.0.0.
Seems like somebody backported it to the 2.64 ebuild. You might have to re-emerge spamassassin.