I'm having a strange issue with email/DNS. Users are having issues sending email to one specific domain (partners.org). Our domain name is ssmh.org. The email system being used is Kerio. I can see the messages sitting in the queue with the error "4.4.3 DNS lookup failed". From what I can tell, DNS is configured correctly on the server. I've ran DNS tests from a couple of online places that check for ns lookup, mx lookup, etc. Everything comes back clean on both domains (sending/receiving). However, if I try to do an nslookup from inside the ssmh.org domain, it does not resolve to partners.org. A nslookup from outside the domain resolves fine to partners.org.
This domain (partners.org) is the only domain that users are unable to send mail too. Mail flow is fine for everywhere else. Initially I thought it may have been a problem with the mail server on the other end, yet when I try to send email to that domain from my personal yahoo account, email gets there without an issue.
Anybody have any ideas/suggestions? this is driving me crazy.
Happy Holidays to all!