XFOR: SMTP Protocol Log Only Shows Connection Established Else

ID: Q190026

The information in this article applies to:

Microsoft Exchange Server, versions 4.0, 5.0, 5.5

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

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

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

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

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

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

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
   
```

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: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT, you should also update your Emergency Repair Disk (ERD).

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

Start Registry Editor (Regedt32.exe).

Locate the DisableReverseResolve value under the following registry key:
```
HKEY_LOCAL_MACHINE\System|CurrentControlSet\Services\MSExchangeIMC
\Parameters\  
```
NOTE: The above registry key is one path; it has been wrapped for readability.

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

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.

Keywords :
Version : WINDOWS:4.0,5.0,5.5
Platform : WINDOWS
Issue type : kbhowto