In Outlook, after you configure an Internet e-mail address as an address to which you do not send any messages in Transport Neutral Encapsulation Format (TNEF), and you designate that address as an alternate recipient for responses, you may discover TNEF formatting in a non-delivery report (NDR).
This situation can be an issue if the e-mail system that hosts the Internet e-mail address does not support TNEF.
To resolve this problem, obtain the latest service pack for Microsoft Exchange 2000 Server. For additional information, click the following article number to view the article in the
Microsoft Knowledge Base:
XGEN: How to Obtain the Latest Exchange 2000 Server Service Pack
Microsoft has confirmed that this is a problem in Microsoft Exchange 2000 Server. This problem was first corrected in Microsoft Exchange 2000 Server Service Pack 2.
To configure an Internet e-mail address as an address to which you do not send any messages that are in TNEF format, click to clear the Always send to this recipient in Microsoft Outlook rich-text format
check box in the E-Mail Properties
dialog box for that address.