Verification of From Address in SMTP Messages

Messages have an address in the From line that is not authentic.

This is done by using Telnet to connect to the mail host on port 25 and by typing RFC-821 SMTP commands to simulate the arrival of a new message. When these messages are received by the Microsoft Exchange Server Internet Mail Service (or Internet Mail Connector, in version 4.0), the address is compared to the Microsoft Exchange Directory. If the address matches a directory entry, the address is replaced in the message header. This means that the spoofed messages look identical to internally sent Exchange Server messages.

To work around this issue:

• On the File menu, click Properties.
  
  If a Headers tab is present, the message was not sent by another Microsoft Exchange Server user in your organization.

Microsoft has confirmed this to be an issue in Microsoft Exchange Server versions 4.0 , 5.0 and 5.5. This issue was corrected in the latest Microsoft Exchange Service Packs. For information on obtaining the Service Packs, query on the following word in the Microsoft Knowledge Base:

For the Exchange Server administrator to enable either version of Microsoft Exchange Server to check the From line, follow these steps:

WARNING: Using Registry Editor incorrectly can cause serious issues that may require you to reinstall Windows. Microsoft cannot guarantee that issues that result 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" online Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" online Help topics in Regedt32.exe. Note that you should back up the registry before you edit.

1. On the Microsoft Exchange Server computer, start Regedt32.exe.
2. Add two values to the IMC Registry Key, under:
   HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/MSExchangeIMC/Parameters
3. On the Edit/Add value menu, add the following:
   
   

         Value Name: TurfDir
         Data Type: REG_SZ
   
         C:\Exchsrvr\Imcdata\Turfdir

   This is the directory where matched messages is stored.
4. On the Edit menu, click Add to add the following:

         Value Name: TurfTable
         Data Type: REG_MULTI_SZ
   
         user1@site.domain
         user2@site.domain

   The Turf Table contains a list of e-mail addresses used to verify the From address on incoming Internet mail. The addresses are not case sensitive and should be entered one per line with no extra spaces or delimiters. If a match is found, the message is saved to the directory specified in the TURFDIR value. In Exchange 5.5 you can add the domain values instead of adding single user names. For example, @site.domain.
5. Restart the Internet Mail Connector service.