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A Looping Condition Was Detected

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  • A Looping Condition Was Detected

    I recently had a problem with looping conditions in Exchange 2003. Hopefully, posting this will save somebody in the future the headache I just experienced.

    An automated job was set up to send e-mails to a distribution group with external users. The message flow should have worked something like this:

    JOB SERVER --> MX (Linux Sendmail server) --> EX2K3 (Exchange 2003 server) --> Distribution List --> MX (Linux Sendmail server) --> External Group Members

    However, the messages weren't being delivered. I sent a test message from my gmail account, and MX delivered it to EX2K3, which resulted in the following error message in the event log:

    Event Type: Error
    Event Source: MSExchangeTransport
    Event Category: NDR
    Event ID: 3017
    Date: 11/20/2009
    Time: 11:30:21 AM
    User: N/A
    Computer: EX2K3
    A non-delivery report with a status code of 5.3.5 was generated for recipient rfc822;[email protected][domain name] (Message-ID <[message ID number]>).

    Causes: A looping condition was detected. (The server is configured to route mail back to itself). If you have multiple SMTP Virtual Servers configured on your Exchange server, make sure they are defined by a unique incoming port and that the outgoing SMTP port configuration is valid to avoid looping between local virtual servers.

    Solution: Check the configuration of the virtual servers connectors for loops and ensure each virtual server is defined by a unique incoming port.
    Naturally, I checked the configuration of the SMTP Virtual Servers and SMTP Connectors, per Microsoft KB 555418. (I think the reference to "status code of 5.4.5" in that article is a typographical error, and should be 5.3.5. Status Code 5.4.5 is not listed in Microsoft KB 284204 ). The SMTP settings in Exchange looked fine.

    Long story short, and after more attempts to figure out what was wrong, I finally noticed that the SMTP address for the Active Directory object for interface -- the name of the distribution group -- was

    [email protected][domain name] instead of
    [email protected][domain name]

    The absence of .ad -- which I failed to notice when I started troubleshooting this problem -- resulted in an error message which led me on a wild goose chase regarding the virtual servers. The fact that everything else was working fine should have been a clue that the problem was with the object in Active Directory, and not with the Exchange server settings.

    Lessons learned:

    (1) Microsoft event log messages are sometimes cryptic and misleading
    (2) Pay attention to details