spammass-milter creates a temporary received-header for each mail. This header does not contain any hint if the sender was authenticated. This causes false-positives for authenticated users.
A fix is available at http://src.linuxhacker.at/products/spamass-milter/spamass-milter-0.3.1/debian/patches/15_spamass-milter-auth-ssf.patch
If this fix is applied, it should be ensured that https://bugs.gentoo.org/show_bug.cgi?id=264304 is applied to!
*** This bug has been marked as a duplicate of bug 265621 ***