I have tested my mail server with the DNSSTUFF. Postmaster and abuse email accounts and I am receiving the same error message.
450 4.1.8 : Sender address rejected: Malformed DNS server reply
postfix log
Jul 27 15:21:23 mail postfix/smtpd[30057]: NOQUEUE: filter: RCPT from adf-a.dnsstuff.com[74.115.12.10]: <dnsstufftools@dnsstuff.com>: Sender address triggers FILTER smtp-amavis:[127.0.0.1]:10024; from=<dnsstufftools@dnsstuff.com> to=<postmaster@XXXX.com> proto=ESMTP helo=<dnsstuff.com>
Jul 27 15:21:23 mail postfix/smtpd[30057]: warning: valid_hostname: invalid character 92(decimal): den-cim-01.solarwinds.com\032
Jul 27 15:21:23 mail postfix/smtpd[30057]: warning: malformed domain name in resource data of MX record for dnsstuff.com: den-cim-01.solarwinds.com\032
Jul 27 15:21:23 mail postfix/smtpd[30057]: warning: valid_hostname: invalid character 92(decimal): adf-cim-01.solarwinds.com\032
Jul 27 15:21:23 mail postfix/smtpd[30057]: warning: malformed domain name in resource data of MX record for dnsstuff.com: adf-cim-01.solarwinds.com\032
Jul 27 15:21:23 mail postfix/smtpd[30057]: NOQUEUE: reject: RCPT from adf-a.dnsstuff.com[74.115.12.10]: 450 4.1.8 <dnsstufftools@dnsstuff.com>: Sender address rejected: Malformed DNS server reply; from=<dnsstufftools@dnsstuff.com>
to=<postmaster@XXXX.com> proto=ESMTP helo=<dnsstuff.com>
dig dnsstuff.com mx +short
10 adf-cim-01.solarwinds.com\032.
20 den-cim-01.solarwinds.com\032.
Postfix MtaRestrictions
reject_non_fqdn_sender
reject_unknown_client
reject_unknown_hostname
reject_unknown_sender_domain
reject_rbl_client zen.spamhaus.org
Any suggestions?
Thanks.