"Connection to Host Lost" Error Message When You Try to Establish a Telnet Session on Port 25

When you try to establish a Telnet session to your Microsoft Exchange computer on port 25, you may receive the following error message: You may not be able to establish a connection to the Exchange 2000 Server Simple Mail Transfer Protocol (SMTP) service. Also, you may experience mail-flow problems with the server.

This issue may occur if the SMTP Virtual Server properties are configured to allow access from a specified list of Internet protocol (IP) addresses, and the IP address of the computer from which you try to access the SMTP service is not listed.

To resolve this issue, modify the SMTP Virtual Server properties to allow access by all computers. To do this, follow these steps:

1. Start Exchange System Manager. To do this, click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. Expand Administrative Groups, and then expand the first administrative group.
   
   Note In this procedure, Administrative groups is enabled. To enable Administrative groups, right-click your organization, click Properties, click to select the Display administrative groups check box, and then click OK.
3. Expand Servers, expand the server that you want, expand Protocols, expand SMTP, right-click Default SMTP Virtual Server, and then click Properties.
4. Click the Access tab, and then click Connection.
5. Click All except the list below.
6. If any computers are listed in the Computers list, verify that you want to deny them access to the SMTP service. If you do not want to deny access to a listed computer, click it and then click Remove.
7. Click OK, click OK, and then quit Exchange System Manager.
8. Restart the SMTP service. To do this, follow these steps:
   1. Click Start, click Run, type cmd in the Open box, and then click OK.
   2. Type net stop smtpsvc, and then press ENTER. You receive the following message:

      The Simple Mail Transport Protocol (SMTP) service is stopping....
      The Simple Mail Transport Protocol (SMTP) service was stopped successfully.
      						

   3. Type net start smtpsvc, and then press ENTER. You receive the following message:

      The Simple Mail Transport Protocol (SMTP) service is starting....
      The Simple Mail Transport Protocol (SMTP) service was started successfully.
      						

   4. Type exit, and then press ENTER.
9. Try to establish a Telnet session to the local host computer on port 25. To do this, follow these steps:
   1. Click Start, and then click Run.
   2. In the Open box, type telnet localhost 25, and then click OK.
   3. Type quit, and then press ENTER to quit the Telnet session.

This same issue may occur with the POP3 protocol (port 110). In this case, you may not be able to establish a Telnet session with the Exchange 2000 server on port 110. To resolve this issue, edit the connection control list for the Default POP3 Virtual Server instead of the Default SMTP Virtual Server. You must restart the Microsoft Exchange POP3 Service after you change the connection control list.