DOCUMENT:Q190026  31-JUL-2002  [exchange]
TITLE   :XFOR: SMTP Protocol Log Only Shows Connection Established Else
PRODUCT :Microsoft Exchange
PROD/VER::4.0,5.0,5.5
OPER/SYS:
KEYWORDS:

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The information in this article applies to:

 - Microsoft Exchange Server, versions 4.0, 5.0, 5.5 
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IMPORTANT: This article contains information about modifying the registry. Before you 
modify the registry, make sure to back it up and make sure that you understand how to restore 
the registry if a problem occurs. For information about how to back up, restore, and edit the 
registry, click the following article number to view the article in the Microsoft Knowledge Base:

   Q256986 Description of the Microsoft Windows Registry

SUMMARY
=======

Some SMTP hosts do a reverse Domain Name Service (DNS) lookup for security
reasons when an SMTP connection is established. If this reverse lookup fails to
resolve properly, they will possibly drop the connection. When this happens, the
SMTP protocol log shows that a connection was established to the host, and then
nothing else is logged for that connection. In addition, the mail may remain in
the Internet Mail Service (Internet Mail Connector in Exchange Server 4.0) queue
with no status.

MORE INFORMATION
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Steps to Test if the Reverse NS-Lookup is Set Up Properly
---------------------------------------------------------

1. Run an Nslookup on the sending domain name as found on the Site Addressing
   tab in the Exchange Server Administrator program. We will use
   mycompany.microsoft.com in the following example.

   Nslookup returns:

      mycompany.microsoft. com preference = 10, mail exchanger =
            mail.mycompany.microsoft.com
      mycompany.microsoft.com nameserver = DNS.mycompany.microsoft.com
      mail.mycompany.microsoft.com internet address = 172.16.0.200
      DNS.mycompany.microsoft.com internet address = 172.16.0.200
  

2. Look at the mail exchange record and find the mail exchanger host
   (mail.mycompany.microsoft.com).

3. Look for the Internet address for this host (172.16.0.200).

4. Do a reverse DNS lookup, which is the IP address typed in reverse order with
   in-addr.arpa at the end. (For our example, you type in
   200.0.16.172.in-addr.arpa. Our example returns:

      200.0.16.172.in-addr.arpa name = mail.mycompany.microsoft.com
  

5. If it does not return the correct information, then the information returned
   will need to be corrected on the DNS server.


It is possible to configure the Exchange Server computer to not do a reverse
lookup. Although Exchange Server will not stop receiving inbound messages if it
cannot properly resolve a reverse lookup, disabling reverse lookup can possibly
speed up performance.

WARNING: If you use Registry Editor incorrectly, you may cause serious problems
that may require you to reinstall your operating system. Microsoft cannot
guarantee that you can solve problems that result from using Registry Editor
incorrectly. Use Registry Editor at your own risk.

You do this by setting the following registry value to 1.

1. Start Registry Editor (Regedt32.exe).

2. Locate the DisableReverseResolve value under the following registry key:

   HKEY_LOCAL_MACHINE\System|CurrentControlSet\Services\MSExchangeIMC
   \Parameters\ 

   NOTE: If you do not find the DisableReverseResolve value, you must add it.

3. On the Edit menu, click DWORD, type 1, and then click OK.

4. Quit Registry Editor.

When reverse resolution is disabled, the Internet Mail Service will no longer
resolve the host name in the "Received From" portion of the SMTP message header.
If the address is in Internet Protocol (IP) form, the address will remain as
such.

Additional query words:

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Keywords          :  
Technology        : kbExchangeSearch kbExchange500 kbExchange550 kbExchange400 kbZNotKeyword2
Version           : :4.0,5.0,5.5
Issue type        : kbhowto

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