DOCUMENT:Q250507  23-FEB-2000  [exchange]
TITLE   :XIMS: NDRs Generated with <> (Blank or Null) Reverse
PRODUCT :Microsoft Exchange
PROD/VER:winnt:5.0,5.5
OPER/SYS:
KEYWORDS:exc5 exc55

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The information in this article applies to:

 - Microsoft Exchange Server, versions 5.0, 5.5 
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SUMMARY
=======

When Exchange Server generates a non-delivery report (NDR), Exchange Server uses
either the System Administrator or Postmaster account of the Internet Mail
Service in the From field of the Multipurpose Internet Mail Extensions (MIME)
message. However, the protocol logging or network trace contains the following
commands:

   HELO <domain>
   250 OK
   MAIL FROM: <>
   250 OK - mail from <>

In other words, the reverse path of the NDRs is null.

MORE INFORMATION
================

This behavior is by design and is in accordance with Request for Comments (RFC)
821, section 3.6. This behavior prevents loops of NDRs that might otherwise
occur if the original sender does not exist.

Excerpt from RFC 821:

   This notification message must be from the server-SMTP at this host. Of
   course, server-SMTPs should not send notification messages about problems
   with notification messages. One way to prevent loops in error reporting is to
   specify a null reverse-path in the MAIL command of a notification message.
   When such a message is relayed it is permissible to leave the reverse-path
   null. A MAIL command with a null reverse-path appears as follows:

   MAIL FROM:<>

If the protocol log or network trace shows that the connection is dropped (SMTP
Error 499) after the MAIL FROM: <> command is issued, troubleshoot the
problem. For additional information about how to troubleshoot the problem, click
the article numbers below to view the articles in the Microsoft Knowledge Base:

   Q198981 XFOR: SMTP Messages Not Being Delivered to Certain Domains

   Q159211 Diagnoses and Treatment of Black Hole Routers

Additional query words:

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Keywords          : exc5 exc55 
Component         : IMS
Technology        : kbExchangeSearch kbExchange500 kbExchange550 kbZNotKeyword2
Version           : winnt:5.0,5.5
Issue type        : kbinfo

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