/usr/share/sendmail/cf/mailer/ is in sendmail-cf 8.14.4-8+deb8u2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/sendmail/cf/mailer/cyrus.m4
/usr/share/sendmail/cf/mailer/cyrusv2.m4
/usr/share/sendmail/cf/mailer/fax.m4
/usr/share/sendmail/cf/mailer/local.m4
/usr/share/sendmail/cf/mailer/mail11.m4
/usr/share/sendmail/cf/mailer/phquery.m4
/usr/share/sendmail/cf/mailer/pop.m4
/usr/share/sendmail/cf/mailer/procmail.m4
/usr/share/sendmail/cf/mailer/qpage.m4
/usr/share/sendmail/cf/mailer/smtp.m4
/usr/share/sendmail/cf/mailer/ssh.m4
/usr/share/sendmail/cf/mailer/usenet.m4
/usr/share/sendmail/cf/mailer/uucp.m4
/usr/share/sendmail/cf/mailer/xagent.m4