DOCUMENT:Q241892 06-AUG-2002 [exchange] TITLE :XFOR: NDR with Error 501 Syntactically Invalid HELO Argument(s) PRODUCT :Microsoft Exchange PROD/VER:winnt:5.0,5.5 OPER/SYS: KEYWORDS:exc5 exc55 ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, versions 5.0, 5.5 ------------------------------------------------------------------------------- SYMPTOMS ======== When sending e-mail to a third-party SMTP server or through a firewall, a non-delivery report (NDR) similar to the following may be generated: Subject: Notification: Outbound Mail Failure - A protocol error occurred. A mail message was not sent due to a protocol error. 501 syntactically invalid HELO argument(s) The message that caused this notification was: CAUSE ===== This error is generated by a third-party SMTP server or firewall. When the Microsoft Exchange Internet Mail Service establishes a connection to a remote host, the Internet Mail Service initiates the SMTP conversation with "EHLO ". If an error is returned, the Internet Mail Service falls back to "HELO ". If the HELO command returns an error, an NDR is generated containing the error. Additional query words: ====================================================================== Keywords : exc5 exc55 Technology : kbExchangeSearch kbExchange500 kbExchange550 kbZNotKeyword2 Version : winnt: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 2002.