plugins/helo: added RFC 5321 notes
plugins/helo: added RFC 5321 notes

smtpd/qpsmtpd,sieutruc/qpsmtpd,msimerson/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,salvis/qpsmtpd,sieutruc/qpsmtpd,msimerson/qpsmtpd,sentinelleader/qpsmtpd-dev,sentinelleader/qpsmtpd-dev,priyadi/qpsmtpd,smtpd/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd