dmarc: skip processing for null sender
dmarc: skip processing for null sender

msimerson/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd,salvis/qpsmtpd,msimerson/qpsmtpd,priyadi/qpsmtpd,sieutruc/qpsmtpd,smtpd/qpsmtpd,smtpd/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,sieutruc/qpsmtpd