e-mail rejected FQHN

[NABILB]

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[19586]: connect from mail.zanadia.com[216.82.93.87]
Oct 22 13:05:24 zimbra postfix/smtpd[19586]: NOQUEUE: reject: RCPT from mail.zanadia.com[216.82.93.87]: 504 5.5.2 <ds5029>: Helo command rejected: need fully-qualified hostname; from=<abcd@zanadia.com> to=<arne@abcdefghi.com> proto=ESMTP helo=<ds5029>

[uxbod]

helo=<ds5029>

your client is presenting itself to the server as ds5029, but due to the AntiSpam measures in place it requires the client to have a FQDN (Fully Qualified Domain Name) eg. ds5029.domain.com.