XIMS: Internet Mail Service Displays SMTP Banner Slowly

After you make a connection to an Exchange Server computer Internet Mail Service on port 25, the Simple Mail Transfer Protocol (SMTP) banner may not be displayed quickly, which may cause certain SMTP applications to time out.

This issue can occur because Exchange Server performs a reverse lookup on all connections. A reverse lookup may take several seconds because of a lack of or incorrectly configured Domain Name System (DNS) servers.

To resolve this issue, increase Internet Mail Service performance by disabling reverse resolution. To do this, you need to edit the registry.

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.

If you use Regedit.exe:

1. Start Registry Editor (Regedt.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC\Parameters
3. On the Edit menu, click New DWORD Value.
4. Type DisableReverseResolve.
5. Under Value data, type 1.
6. Quit Registry Editor.

If you use Regedt32.exe:

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC\Parameters
3. On the Edit menu, click Add Value, and then add the following registry value:
   Value Name: DisableReverseResolve
   Data Type: REG_DWORD
   Radix: Binary
   Value: 1
4. Quit Registry Editor.

Reverse resolution occurs when the name of the host that delivered an incoming SMTP message is resolved and placed in the message header by the Internet Mail Service. When reverse resolution is disabled, the Internet Mail Service does not resolve the host name in the upper-most Received From field of the SMTP message header. If the address is in Internet Protocol (IP) form, it remains in IP form.