Microsoft KB Archive/250507

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XIMS: Non-Delivery Reports Generated with <> (Blank or Null) Reverse Path

Article ID: 250507

Article Last Modified on 10/28/2006


  • Microsoft Exchange Server 5.0 Standard Edition
  • Microsoft Exchange Server 5.5 Standard Edition

This article was previously published under Q250507


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
250 OK - mail from <>

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


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:


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:

198981 XFOR: SMTP Messages Not Being Delivered to Certain Domains

159211 Diagnoses and Treatment of Black Hole Routers

Keywords: kbinfo KB250507