How to Configure Exchange 2000 to Not Resolve External Email Addresses

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Exchange Server 2003 does not resolve e-mail addresses that originate externally. Therefore, when an anonymous user attempts to send mail spoofing a user's identity, Exchange Server will not resolve the sending address in the From line to its display name. Instead, for a user named Ted, ted@example.com will appear in the From line of the e-mail. If your users understand this difference, they can at least identify spoofed mail.

Before You Begin

Be cautious when you select the servers on which you want to enable this setting. If you change the behavior on the default SMTP virtual server, and there are multiple servers in your organization, all internal mail that originates on other Exchange 2000 servers is also affected. Therefore, because Exchange 2000 Server uses SMTP to route internal mail between servers, you may want to create a new SMTP virtual server, or perhaps to apply this setting only on an incoming SMTP bridgehead server.

Before you perform the procedure in this topic, read Configuring Filtering and Controlling Spam and How to Verify That Exchange 2003 is Configured to Not Resolve Anonymous Mail.

The following permissions are required to perform this procedure:

  • Member of the local administrators group and a member of a group that has had the Exchange Administrators role applied at the administrative group level

Procedure

To configure Exchange 2000 Server to not resolve e-mail addresses that originate externally

  1. Start Registry Editor: Click Start, click Run, type regedt32, and then click OK.

  2. Locate or create the following key in the registry (where 1 is the SMTP virtual server number):

    HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/ MsExchangeTransport/Parameters/1

    Note

    You may need to create both the Parameters key and the 1 key.

  3. On the Edit menu, click Add Value, and then add the following registry value:

    Value name: ResolveP2
Data type: REG_DWORD

  4. Use the following flags to determine which value to use:

          Field                  Value
      -----------            -----
      FROM:                  2
      TO: and CC:            16
      REPLY TO:              32

    To determine the value that you want to use, add the values for all of the elements that you want to be resolved. For example, to resolve all of the fields except the sender, type 48 (16+32=48). To resolve only the recipients, type only 16. By default, Exchange 2000 Server resolves everything. You can specify this behavior either by removing the key or by setting the value with this formula: 2+16+32=50.

  5. Quit Registry Editor.

  6. Restart the SMTP virtual server.