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Q202765: XIMS: Using IMS Mail: "503 Sender Already Specied"

Article: Q202765
Product(s): Microsoft Exchange
Version(s): winnt:4.0,5.0,5.5
Operating System(s): 
Keyword(s): 
Last Modified: 06-JUN-1999

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The information in this article applies to:

- Microsoft Exchange Server, versions 4.0, 5.0, 5.5 
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SYMPTOMS
========

Occasionally, messages from Exchange Server through the Internet Mail Service
(Internet Mail Connector in version 4.0) to a remote SMTP e-mail domain are
rejected. A non-delivery report (NDR) is returned to the sender with the
following error message:

  503 Sender already specified.

CAUSE
=====

Exchange Server makes connections to remote SMTP mailers or relay hosts to
deliver SMTP mail. If more than one message is queued to a remote domain,
Exchange Server can send multiple messages during a single connection. If the
remote SMTP server is not RFC-compliant, it improperly rejects the delivery of a
second message from the Internet Mail Service during the course of a single
connection. Then it sends the NDR mentioned above.

The sequence of events is as follows:

- Exchange Server's Internet Mail Service finishes the first message and
  receives a "250 OK" acknowledgement that the message was accepted.

- The Internet Mail Service then attempts to send the second message in this
  same connection by sending the MAIL FROM command.

- The remote host improperly rejects the message with the "503 Sender already
  specified" error message. This is not RFC 821 compliant according to section
  4.1.1.

WORKAROUND
==========

Although this is a problem with the remote system, you can correct the problem
by setting the Internet Mail Service to send only one message for each
connection. This is a global setting that affects the performance of the
Internet Mail Service because it no longer sends multiple messages during a
single connection to any remote domain. This may be a minor issue for some
e-mail networks and a preferable option to the above problem.

Additional query words:

======================================================================
Keywords          :  
Technology        : kbExchangeSearch kbExchange500 kbExchange550 kbExchange400 kbZNotKeyword2
Version           : winnt:4.0,5.0,5.5
Issue type        : kbprb

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