Im using my own DNS server ( not using ZCS dnscache )
Here is nslookup from ZCS server :
[zimbra@v-kajmany ~]$ nslookup
> server 149.156.208.49
Default server: 149.156.208.49
Address: 149.156.208.49#53
> post.pl
Server: 149.156.208.49
Address: 149.156.208.49#53
Non-authoritative answer:
Name: post.pl
Address: 212.85.96.51
>
> 89.161.251.167
Server: 149.156.208.49
Address: 149.156.208.49#53
Non-authoritative answer:
167.251.161.89.in-addr.arpa name = post.pl.
Authoritative answers can be found from:
251.161.89.in-addr.arpa nameserver = dns.home.pl.
251.161.89.in-addr.arpa nameserver = dns3.home.pl.
251.161.89.in-addr.arpa nameserver = dns2.home.pl.
dns.home.pl internet address = 46.242.149.10
dns.home.pl internet address = 46.242.149.11
dns2.home.pl internet address = 46.242.149.20
dns2.home.pl internet address = 46.242.149.21
dns3.home.pl internet address = 46.242.149.31
dns3.home.pl internet address = 46.242.149.30
> mail.kpu.ac.kr
Server: 149.156.208.49
Address: 149.156.208.49#53
Non-authoritative answer:
Name: mail.kpu.ac.kr
Address: 210.93.48.155
> 210.93.48.153
Server: 149.156.208.49
Address: 149.156.208.49#53
Non-authoritative answer:
153.48.93.210.in-addr.arpa name = mail.kpu.ac.kr.
Authoritative answers can be found from:
48.93.210.in-addr.arpa nameserver = rev2.kornet.net.
48.93.210.in-addr.arpa nameserver = rev1.kornet.net.
rev1.kornet.net internet address = 211.216.50.170
rev2.kornet.net internet address = 211.216.50.180
As for RBLs im using :
zimbraMtaRestriction: reject_rbl_client b.barracudacentral.org
zimbraMtaRestriction: reject_rbl_client zen.spamhaus.org
zimbraMtaRestriction: reject_rbl_client bl.spamcop.net
zimbraMtaRestriction: reject_rhsbl_client dbl.spamhaus.org
zimbraMtaRestriction: reject_rhsbl_client multi.uribl.com
zimbraMtaRestriction: reject_rhsbl_client multi.surbl.org
zimbraMtaRestriction: reject_rhsbl_reverse_client dbl.spamhaus.org
zimbraMtaRestriction: reject_rhsbl_sender multi.uribl.com
zimbraMtaRestriction: reject_rhsbl_sender multi.surbl.org
zimbraMtaRestriction: reject_rhsbl_sender rhsbl.sorbs.net
zimbraMtaRestriction: reject_rhsbl_sender dbl.spamhaus.org
Problem is not intermittent is mail from post.pl come from ip 212.85.96.51, there is no problem, and zimbra dont comaplain about unknow hostname, but if it comes from 89.161.251.167 its rejected. Cant say about kpu.ac.kr becose they only mailed us once. Most of emails ( if its not spam ) dont have thiss kind of a problem, its only when ip from where mail came from dont match the domain, like in this case. post.pl = 212.85.96.51 and mail came from ip : 89.161.251.167
Only thing that came in mind is that they should just point that domain name to another ip addres. Like google :
host gmail.com
gmail.com has address 172.217.20.197
gmail.com has IPv6 address 2a00
401b:803::2005
gmail.com mail is handled by 40 alt4.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 10 alt1.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 30 alt3.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 20 alt2.gmail-smtp-in.l.google.com.
gmail.com mail is handled by 5 gmail-smtp-in.l.google.com.