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No SMTP log of possible relay?

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  • No SMTP log of possible relay?

    Morning all,

    Interesting one for you here, a client of ours has an Exchange 2007 server up and running and by all accounts is running well. Recently they set up a contact form on they're web site that sends an email, this email is not being received by the exchange server and there is no record of it in the SMTP logs. I got in touch with the web designer how advised me it was sending using a standard PHP function... I then asked him to add my personal email as a second recipient.

    Ok to cut a long story short, web server sends email to: [email protected] & [email protected] from: [email protected] reply address: [email protected]

    My personal email receives the email ok.

    Exchange server does not receive the email and there is no record of it in SMTP logs. Theory is that exchange sees it as relaying as it hosts all email for Would this be a valid assumption? Why would it not log anything? I'm a bit lost on this and where to go from here...

    hope that all makes sense



    Just realised if I telnet to the server & try to send an email to: [email protected] (does exist) from: [email protected] (not exist) reply address: [email protected] (not exist) then it should prove my theory..... Not what I expected, the mail server accepted it and delivered it to the correct mail box, and its in the SMTP logs.....
    Last edited by QuattroDave; 24th January 2013, 14:52. Reason: additional info

  • #2
    Re: No SMTP log of possible relay?

    Your presumption that the email is being blocked as a relay attempt is incorrect.

    An external entity sending an email to an email address for which the Exchange server IS authoritative for is NOT relaying. This is exactly how SMTP works. The sender address doesn't need to be a valid address and as such Exchange has no way to know if the sender address is valid or not. Exchange simply accepts the email and delivers it internally. In the case of the web site, it is sending email TO Exchange.

    In the case of a relay, an external entity would send an email THROUGH the Exchange server to an email address that the Exchange server IS NOT authoritative for.

    Without getting into the vagaries of authenticated SMTP, connection filtering, recipient filtering, etc. here's a basic rundown:

    External sender--->Exchange--->Internal recipient = No Relay

    External sender--->Exchange--->External recipient = Relay


    • #3
      Re: No SMTP log of possible relay?

      Thanks for your reply,

      That makes perfect sense.

      That then begs the question, why can the web server send emails to me and not the exchange server?

      The one thing that bothers me is there is nothing logged in SMTP logs from the web sever, all other incoming emails are logged, which sort of suggests either the web server isn't sending properly or its somehow sending to the wrong IP / MX record.....? I take it the web server uses DNS just like everything else....?



      • #4
        Re: No SMTP log of possible relay?

        Without knowing what code is being used to send the email it's hard to say.

        You could start by checking the DNS settings on the web server, then run nslookup on the web server to check the MX record for the email address domain, then try to telnet from the web server to the Exchange server and send a test email to the recipient. Those steps should hopefully give you a clue as to what's happening (or not happening).


        • #5
          Re: No SMTP log of possible relay?

          This issue is now in the hands of the web designer.
          My theory is that the website is using a mailer table or static/defined route and is not performing a lookup from DNS. I'll post back with the findings...