This article details various connection issues to Microsoft Exchange via the POP3 protocol and offers solutions.

Symptoms

  • Unable to connection to POP3 - connection refused
  • A connection is started except it hangs with no server banner/header (beginning with +OK) is shown.
  • An incorrect password error is shown (-ERR Unknown user name or bad password) despite is being known that the password is correct.

Resolution

Attempt the following fixes in order, whilst re-attempting the connection each time.

  1. Ensure that the virtual server/service is running. From cmd type services.msc and select the 'Microsoft Exchange POP3' service and ensure that it is started and in particular not disabled.
  2. Restart the POP3 service. From the same window as details above right click the 'Microsoft Exchange POP3' service and choose restart.
  3. Eliminate firewalling or other network issues as a possibility. try connecting to it locally. From the server itself in cmd type telnet 127.0.0.1 110 where 110 is the port that the service is listening to.
  4. Depending on the configuration of your environment it may be required to use the extended syntax for the username you are using. The extended syntax is domain\\username\\alias. The mailbox alias is by default it by default the same as the username and can be checked on the Exchange General tab in a Exchange-enabled Active Directory Users and Computers.
  5. Check that the POP3 virtual server is listening to the correct port: Open Exchange System Manager, navigate to the server > Protocols > POP3 > Default POP3 Virtual Server and choose properties. Click on the General tab followed by Advanced. Ensure that the server is listening to the default port - 110 - or the port where a connection is being attempted.
  6. Ensure that no other applications are listening to the port that POP3 is listening to: From cmd type netstat -abn to ascertain which applications are listening to which ports. If any apps are listening to the same port this would cause the connection to fail of course.
  7. Ensure no connection control parameters have been set: From Default POP3 Virtual Server properties click on the Access tab followed by Connection. If the list is empty and 'Only the list below' is selected this can cause the connection to fail where the connection is started but no server banner/header (beginning +OK) is ever displayed.

See Also

Category:Exchange