Emails getting rejected by wrong recieving server, when resent they go fine 1

[tpulley]

This is a strange issue. This started a couple of months ago. Users send emails/reply to emails and the emails are rejected by remote side, the remote side has a tottaly different dns name. Users can resend and sometimes they go through the first time sometimes they have to do it twice. They always go through. This is to several different email domains. Some emails addresses have never been sent before some have. No particular rhyme or reason.

I have changed the dns server forwarding to three different ones. Some dns server addresses I use in other sites and they work flawlessly there.

Any ideas?

 

[Zelandakh]

what is the rejection?
What does your internal DNS resolve their MX record to and is that accurate?
Does your smarthost have a problem?
Any error messages in the event logs?

 

[tpulley]

No smarthost being used. The rejections are for example: Email sent to two@123.com the rejection states that fat.com domain doesn't know of a user on this mailbox. Others are the 5.7.1 email address failure to send. Internal nslookup (dns) does resolve to the correct mailserver. The strangest things is sometimes they get through sometimes they don't.

 

[ShackDaddy]

How many MX records exist for the target domain? If there are more than one with the same priority, try sending an email to each of them via Telnet and see if one of them rejects and the other doesn't.

Dave Shackelford
ThirdTier.net
TrainSignal.com

 

[tpulley]

There are several domains this is happening to not just one or two. Maybe 20? It makes me think its on our side but I cannot find out what it is. I can telnet to the mx record fine with everyone I have tried.

 

[ShackDaddy]

It does sound like it's on your side. You may already be using this, but just in case: do you know there's a setting in Exchange 2010 to explicitly use a specific DNS server for outbound mail even if the NIC is configure to point to an internal server for DNS?

On the Send Connector's Network tab you'd check that box saying to use external DNS lookup settings, and you'd configure the DNS servers by going to the Server's container in the EMC, getting properties on your Hub transport server, and configuring the External DNS Lookups tab.

That way you can totally control what your hub transport server is doing on the DNS-lookup side of things and rule out how your internal DNS server and its forwarding is configured.

Dave Shackelford
ThirdTier.net
TrainSignal.com