Our e-mails to a Zimbra client keep getting rejected. below is the log from Zimbra. We checked and all our settings seem to be correct, and our e-mails get delivered fine to most e-mail servers. Any ideas?
Oct 22 13:05:23 zimbra postfix/smtpd: connect from mail.zanadia.com[220.127.116.11]
Oct 22 13:05:24 zimbra postfix/smtpd: NOQUEUE: reject: RCPT from mail.zanadia.com[18.104.22.168]: 504 5.5.2 <ds5029>: Helo command rejected: need fully-qualified hostname; from=<firstname.lastname@example.org> to=<email@example.com> proto=ESMTP helo=<ds5029>