Problem: Spamassassin is not properly filtering domains such as link, click, xyz, science, and similar.
Solution: Your Registrar Boundaries file is out of date.
In Ubuntu, go to /usr/share/perl5/Mail/SpamAssassin/Util/
Use: wget svn.apache.org/repos/asf/spamassassin/trunk/lib/Mail/SpamAssassin/Util/RegistrarBoundaries.pm (It will probably download as RegistrarBoundaries.pm.1)
cp RegistrarBoundaries.pm to RegistrarBoundaries.pm.old
cp RegistrarBoundaries.pm.1 to RegistrarBoundaries.pm
sudo service spamassassin restart