DOCUMENT:Q280118 11-APR-2001 [exchange] TITLE :XFOR: Non-Delivery Report with "501 Sender Domain Must Exist" Me PRODUCT :Microsoft Exchange PROD/VER::5.5 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, version 5.5 ------------------------------------------------------------------------------- SUMMARY ======= Some Microsoft Exchange e-mail messages generate a non-delivery report (NDR) with the message "501 sender domain must exist." This behavior occurs because the sender domain is not registered on the Internet. Check with your Internet service provider (ISP) or Domain Name System (DNS) administrator to verify that the sender's domain has MX records on the Internet. MORE INFORMATION ================ Some other (non-Exchange Server) mail systems check the sender's e-mail domain to prevent junk e-mail (spam). This is called performing a reverse lookup. When these mail systems receive an SMTP connection, they attempt name resolution based on the address in the From field. If the address in the From field cannot be resolved by DNS, the receiving mail system responds with "501 Sender domain must exist," and closes the connection, causing the NDR. As a test, try to telnet the destination server over port 25. You receive the following results mail from:test@DomainTest.com 501 test@DomainTest.com... Sender domain must exist and the connection generates the NDR. Then, try opening a telnet session over port 25 from a domain that is known to work. The following results are returned: mail from:test@Microsoft.com 250 test@Microsoft.com... Sender ok Additional query words: ====================================================================== Keywords : Technology : kbExchangeSearch kbExchange550 kbZNotKeyword2 Version : :5.5 Issue type : kbinfo ============================================================================= 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 2001.