After Exchange 2000 Server Service Pack 1 (SP1) is installed, Exchange 2000 Server administrators can enable the ResolveP2 functionality. For additional information about ResolveP2 functionality, click the article numbers below to view the articles in the Microsoft Knowledge Base: NOTE: The registry key definitions have changed between Exchange Server 5.5 and Exchange 2000; the following instructions only apply to Exchange 2000.

The ResolveP2 registry setting contains information that Exchange 2000 can use to "resolve" specified addresses in a mail message body (referred to as "P2"), if those users exist in the Exchange 2000 directory. A resolved address is displayed as follows when the mail message is received by a mail client, such as Microsoft Outlook: An unresolved address is displayed as follows: If you double-click a resolved address in the client, the Exchange 2000 directory information is displayed. An unresolved address simply displays the Simple Mail Transport Protocol (SMTP) address. Because this is the resolution behavior for internal addresses, an external resolved address can lead a mail user to believe that mail originated from within the local domain or organization. If you enable the ResolveP2 setting, educated users can tell the difference between internal and external mail.

Set the ResolveP2 key on the server that receives mail from the Internet. If you are upgrading from Exchange Server 5.5, you still need to use the following steps because the Exchange Server 5.5 keys are not used by Exchange 2000.

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.

To set the ResolveP2 key:

1.	Start Registry Editor (Regedt32.exe).
2.	Locate or create the following key in the registry (where 2 is the SMTP virtual server number): HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/MsExchangeTransport/Parameters/2 You might need to create the "Parameters" key and the 2 key as well.
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 Decimal 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 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 that you specified in step 2.

Use careful consideration when you select the servers that you want to enable this setting on. If you change the behavior on the default SMTP virtual server (generally virtual server instance 1, except on a cluster) and there are multiple servers, all internal mail that originates on other Exchange 2000 servers is also affected. Therefore, you may want to create a new SMTP virtual server, or only apply this setting on an incoming SMTP bridgehead server, because Exchange 2000 uses SMTP to route internal mail between servers.