Two 2003 exchange servers on differenet subnets can not send e-mail to each other

Posted on 2007-10-02
Last Modified: 2012-05-05
Here is a very perplexing issue:

Two exchange 2003 servers are sitting in different domains, different subnets, and different external IP addresses but are connected to the same layer 2/3 switch behind the same firewall and same ISP.

Any exchange servers outside of the firewall can send e-mail to either exchange server behind the firewall without issue.

Any exchange server behind the firewall can send e-mail to any exchange server beyond the firewall without issue.

The issue is you can not send e-mail for one exchange server behind the firewall to the other one behind the firewall or vise versa.

Both exchange servers behind the firewall can ping each other
You can telnet to each using the internal IP addresses on port 25
You can not telnet to each other using their external IP addresses on port 25

The firewall looks like its doing a loop back which from what I know should be fine but seems to cause this not to work for some reason. So while tech support for the firewall work on it from their side my thought was just make it so the two exchange servers behind the firewall get the MX address from the local windows 2003 DNS server that points to each others local address.

Well even if we create a DNS zone with an mx record that points to the internal IP addresses for the exchange servers  exchange still does cant send mail.

We noticed that when we query the local Windows 2003 DNS server we only get the stub returned not the real MX record.

We have used the SMTPDIAG tool and it fails too when we try to send from one internal exchange server to the other internal exchange server.

Any ideas?
Question by:jkolaski
    LVL 104

    Accepted Solution

    Skip using MX records.
    What I do in this scenario, particularly as they can telnet to each other, is to use smtp connectors.
    Create one in each Exchange org.
    Set it to use a smart host, remember if the DNS doesn't work and you use an IP address, it needs to be in [ ] - so [].
    Then on the address space tab enter the domain/s that the other server is responsible for.

    I would actually do that despite the firewall configuration.


    Author Comment

    Will give it a try in the morning.

    Author Comment

    Your idea worked and I will accept that as the solution but do you have any idea why a windows 2003 dns server would not return the mx record and only the stub?
    LVL 104

    Expert Comment

    It shouldn't be doing that. I would check whether the DNS entry is configured correctly. It isn't something I have seen Windows DNS do before.


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