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Unable to Connect to External Email Server

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  • Unable to Connect to External Email Server

    Here's the situation, we have SBS 2008 with Exchange 2007 fully configured to handle all our email. It's been working great with the exception of 1 domain. When ever we try to send email to this particular domain, we get an error.

    So in the course of normal troubleshooting I decided to telnet to this external email server from our SBS box. Telnet failed on port 25. I thought that we were just having Internet troubles, but then I stepped over to a Windows XP box in the same office as the SBS box and tried it. Connected fine on port 25. I found it a little odd that the SBS couldn't connect and XP worked just fine.

    I've been in contact with the sys admin that runs the external server. He has run into this issue before with SBS 2008 machines connecting to his server. He has never been able to find a solution. He had an inkling that it was somehow related to the way SBS 2008 handles DNS lookups with IPv6 enabled, so I disabled IPv6 on the SBS machine and tried again. Same issue.

    So this brings me to my question:

    What are possible reasons I cannot telnet to this external email server from SBS 2008 but I can connect fine from Windows XP?

    I'm guessing there's something funky with the way SBS 2008 does TCP connections. I would say telnet connections, but that would imply only telnet is effected, when Exchange is also effected. This would lead me to believe it's a problem with the network stack itself as opposed to either program. I would suspect this could be verified with Vista. I know that Server 2008 is based on Vista code, and I would assume they use the same network stack. I might have to try connecting from a Vista machine to confirm.

    We're using a fully updated SBS 2008 install and the external mail server is Windows XP with MDaemon.

    We've both been working on this for weeks and have nothing, so if someone can swoop in and solve the issue I'd really appreciate it!

  • #2
    Re: Unable to Connect to External Email Server

    What error does the NDR give?

    What MX records do you get for the domain using NSLOOKUP on the server and on the XP machines? Are they the same?
    Gareth Howells

    BSc (Hons), MBCS, MCP, MCDST, ICCE

    Any advice is given in good faith and without warranty.

    Please give reputation points if somebody has helped you.

    "For by now I could have stretched out my hand and struck you and your people with a plague that would have wiped you off the Earth." (Exodus 9:15) - I could kill you with my thumb.

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    • #3
      Re: Unable to Connect to External Email Server

      Any firewall enabled on the 2008 box???

      Any virus software installed on the 2008 box???

      Do you have a hardware firewall between the SBS box and the internet that may have a restriction set on it??

      It is possible that either a hardware/software firewall or AV program is stopping your telnet connection to the external machine.


      • #4
        Re: Unable to Connect to External Email Server

        The NDR given is:

        #550 4.4.7 QUEUE.Expired; message expired ##

        Not exactly helpful. The queue reports this error:

        451 4.4.0 Primary target IP address responded with: "4.2.1 Unable to connect." Attempt failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.

        This is the only mail server reported by the MX record.

        I also enabled verbose SMTP logging and got this error:

        Error Code: 10060, Error Message: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to response x.x.x.x:25

        MX records for the domain are the same on both the SBS and XP machines. I also tested at home and got the same MX record.

        Basic Windows firewall and hardware SonicWall on the network. Port 25 works to other hosts and there are no error messages in the logs. Server currently does not have AV installed.

        I did some testing from home and found out something interesting. I can telnet fine with any XP machine. I can also telnet fine with Windows 7 RC. If I fire up Vista Business (same network stack as Server 2008, telnet fails. In all cases(XP, Vista, 7), I can telnet fine on port 25 to other hosts.

        I also created a basic Python program to test a socket connection. If I run this in Vista I can get to other hosts on port 25 fine, but cannot connect to the external email server in question.

        This would lead me to believe that the request for connection generated by the Vista/Server 2008 network stack is just plain rejected by MDaemon. Now, this assumes that the Windows 7 stack is different from Vista/Server 2008 somehow and that Python uses the OS network stack (which really is the only thing that makes sense).

        Anyone want to point out problems with the testing? I don't want to start digging into the actual request packets if that's not the way to go.

        Thanks for the replies so far!