DOCUMENT:Q202765 06-JUN-1999 [exchange] TITLE :XIMS: Using IMS Mail: "503 Sender Already Specied" PRODUCT :Microsoft Exchange PROD/VER:winnt:4.0,5.0,5.5 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, versions 4.0, 5.0, 5.5 ------------------------------------------------------------------------------- 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 ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 1999.