DOCUMENT:Q245787 04-DEC-1999 [exchange] TITLE :XFOR: SMTP Error Message: 550 Invalid Domain PRODUCT :Microsoft Exchange PROD/VER:winnt:4.0,5.0,5.5 OPER/SYS: KEYWORDS:exc4 exc5 exc55 ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, versions 4.0, 5.0, 5.5 ------------------------------------------------------------------------------- SYMPTOMS ======== If you send outbound Simple Mail Transfer Protocol (SMTP) mail, a non-delivery report (NDR) similar to the following is displayed: 550 Invalid Domain. The following NDR is also logged in the application event log: Event ID: 4031 Source: MSEXCHANGEIMC Description: The message could not be delivered. The destination server reported: 550 Invalid Domain. CAUSE ===== This problem may be caused by a Domain Name System (DNS) record that points to the wrong mail host for a certain domain. This incorrect DNS information causes Exchange Server to connect to the wrong mail host when you try to send mail to a recipient in another domain, which generates the error message in the "Symptoms" section of this article. This problem may also be caused by the incorrect configuration of an "echo firewall." The echo firewall is an advanced device that verifies every command that is sent to the Exchange Server computer. This type of firewall cannot be a Network Address Translation (NAT) or packet-filter device. If you incorrectly configure this firewall so that it does not accept mail from a domain that it needs to accept mail from, the error message in the "Symptoms" section of this article may also be displayed. The mail never resides on the firewall, but passes through it. RESOLUTION ========== Use the NSLookup utility to make sure that the MX and A records of the Exchange Server domain on the Internet are correct. If the problem is related to the incorrect configuration of an echo firewall, then correct the configuration of the firewall. MORE INFORMATION ================ The error message in the "Symptoms" section of this article is closely related to the following Exchange Server generated error message: 550 Relaying is prohibited The message route of this topology is: Sending Exchange Server ----- Internet ------ Firewall ----- Mailhost The SMTP conversation of this problem may look like the following log: A connection to 10.1.1.25 was established. <<< IO: |220 firewall.expedia.com Generic SMTP handler <<< 220 firewall.expedia.com Generic SMTP handler >>> EHLO ExchangeSending.microsoft.com <<< IO: |500 Command unrecognized <<< 500 Command unrecognized >>> HELO ExchangeSending.microsoft.com <<< IO: |250 firewall.expedia.com talking to mailhost.expedia.com [157.5.1.4]) <<< 250 firewall.expedia.com talking to mailhost.expedia.com ([157.5.1.4]) >>> MAIL FROM: <<< IO: |250 : Sender Ok <<< 250 : Sender Ok >>> RCPT TO: <<< IO: |550 Domain invalid <<< 550 Domain invalid >>> QUIT <<< IO: |221 firewall.microsoft.com closing connection. Goodbye! Additional query words: 4031 3010 Invalid Raptor Secure Gateway ====================================================================== Keywords : exc4 exc5 exc55 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.