DOCUMENT:Q146157 19-DEC-1999 [exchange] TITLE :XFOR: Should Have Exclusive Access to Port 25 PRODUCT :Microsoft Exchange PROD/VER:winnt:4.0 OPER/SYS: KEYWORDS:kbusage exc4 exc5 exc55 ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, version 4.0 ------------------------------------------------------------------------------- SYMPTOMS ======== The Microsoft Exchange Internet Mail Connector (IMC) requires exclusive use of TCP port 25 to successfully transport SMTP mail. If another program reserves port 25, the IMC may start without error, but no incoming mail will be accepted. CAUSE ===== The Internet Mail Connector uses TCP port 25 for inbound SMTP mail as defined by RFC-821. For inbound SMTP mail, the IMC monitors port 25 for incoming connections from other SMTP hosts. The IMC will answer all incoming SMTP calls if it is the first or only SMTP service running. If another SMTP service is running and set to receive mail, the Internet Mail Connector will start without error, but incoming mail will not be delivered to the Information Store. Incoming SMTP mail may be delivered to the third party program's delivery queue, or it may be rejected and returnedto the originating host. The IMC may be able to deliver outbound mail even if another SMTP host is monitoring port 25 for incoming mail. Multiple outbound connections are possible, and when outbound mail is to be delivered, the IMC opens one or more connections to port 25 to connect to other SMTP hosts. RESOLUTION ========== Do not run third party SMTP applications on any Microsoft Exchange server that is running the Internet Mail Connector service. You can verify if you have another SMTP service running by using the Windows NT telnet program. To test the connection, run telnet from the Windows NT command prompt specifying the IP address of the server running the Internet Mail Connector, for example: telnet xxx.45.66.77 25 By default, the IMC will respond with a greeting similar to: 220 imc.company.com service ready If the response is worded differenty, you may have a third party SMTP service that is running that you should disable to allow the Internet Mail Connector to transfer SMTP mail. Additional query words: imc port25 ====================================================================== Keywords : kbusage exc4 exc5 exc55 Technology : kbExchangeSearch kbExchange400 kbZNotKeyword2 Version : winnt:4.0 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.