ssmtp.conf still/again is world-readable by default.
I was able to fix this by doing (as root):
chmod -R 2750 /etc/ssmtp/
chown root:mail /etc/ssmtp/
chmod g+s /usr/sbin/ssmtp
chmod g+s /usr/sbin/sendmail
chmod g+s /usr/sbin/mailq
Though I might have added a +s more than strictly necessary.
I also did
dpkg-statoverride --add root mail 2750 /etc/ssmtp
dpkg-statoverride --add root mail 2750 /etc/ssmtp/ssmtp.conf
dpkg-statoverride --add root mail 2750 /etc/ssmtp/revaliases
dpkg-statoverride --add root mail 2755 /usr/sbin/ssmtp
dpkg-statoverride --add root mail 2755 /usr/sbin/sendmail
dpkg-statoverride --add root mail 2755 /usr/sbin/mailq
And now it all seems to be working fine.
Sincerely,
Thom Wiggers