XCLN: Troubleshooting POP3 Connections to Exchange Server (161118)

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Basic Troubleshooting

If you are unable to connect to the Internet Mail Server from an e-mail client using POP3, use the following steps to troubleshoot the problem. After performing each step, check to see if the issue has been resolved.

1. Verify that the e-mail client is POP3-compliant. Many e-mail clients are not POP3-compliant. In particular, many newer e-mail clients support Internet Mail Access Protocol version 4 (IMAP4). Microsoft Exchange Server versions 4.0 and 5.0 do not support IMAP4. For IMAP4 support you must upgrade to Microsoft Exchange Server version 5.5. Microsoft Exchange Server supports POP3 as defined in the RFC 1725, RFC 1734, RFC 1939, and RFC 1953 specifications.
2. Use the Telnet tool to connect to the Microsoft Exchange Server. To do so, follow these steps:
   
   
   1. On the e-mail client, start Telnet. For the host name, type the name of the Microsoft Exchange Server computer, and for the port type, type 110. If a "term type" is requested, do not type anything. For example, type the following command to start Telnet:

      telnet server 110

      where server is the name of the Microsoft Exchange Server computer. If you are running Windows 95, Windows NT Workstation, or Windows NT Server, you can type the above command at a command prompt or in the Run dialog box. If you are running Windows NT Workstation or Windows NT Server version 3.51, you can open the Run dialog box from the File menu or the task list.
      
      When you type the above command and then press ENTER, a message similar to the following should be displayed:

      +OK Microsoft Exchange POP3 server version 5.0.1457.10 ready

      NOTE: The version number might be different, but it should be 5.0.1457.10 or later.
   2. Enable local echo for the current Telnet session. To do so, on the Terminal menu, click Preferences, click the Local Echo check box to select it, and then click OK.
   3. Type the following command, and then press ENTER: user domain\username\mailbox where domain is the name of the domain in which the user's account is located, username is the user name, and mailbox is the user's mailbox. Note that the mailbox portion of the above command is only necessary if it is different from the username portion. When you press ENTER, "+OK" (without quotation marks) should be displayed.
   4. Type the following command, and then press ENTER:

      pass password

      where password is the user's password. When you press ENTER, the following message should be displayed:

      +OK User successfully logged on

   5. To determine if the user has new messages, type "stat" (without quotation marks), and then press ENTER. After you press ENTER, the following message should be displayed:

      +OK xyyyy

      where x is the number of new messages and yyyy is the total size of the messages in bytes. This is known as a "drop listing."
   6. To end the Telnet session, type "quit" (without quotation marks), and then press ENTER. When you press ENTER, a message similar to the following should be displayed:

      +OK Microsoft Exchange POP3 server version 5.0.1457.10 signing off

NOTE: The above POP3 commands can only be used to troubleshoot problems when you attempt to receive messages. A POP3 client uses Simple Mail Transfer Protocol (SMTP) to send messages. For information about how troubleshoot problems when you attempt to send messages, please see the following article in the Microsoft Knowledge Base:

Additional Troubleshooting

If the problem still occurs, perform these steps. After performing each step, check to see if the issue has been resolved.

1. Verify that the POP3 protocol is enabled for the site Protocols container and the Protocols container on the server.
2. Verify that POP3 support is not disabled for the user's mailbox.
3. Verify that the client can ping the server using the server's Internet protocol (IP) address and the server's computer name.
4. Run the Rpings.exe tool that is located on the Microsoft Exchange Server CD-ROM. Rpings.exe runs on the server; a client program must also be run on the client. If you are running Windows or Windows for Workgroups version 3.x, run Rpingc16.exe on the client. If you are running Windows 95, Windows NT Server, or Windows NT Workstation, run Rpingc32.exe on the client.
   
   NOTE: The Rpings.exe tool is used to determine if the client can connect to the server using remote procedure call (RPC). POP3 clients do not connect to the Microsoft Exchange Server computer using RPC.
5. Try to use the Microsoft Exchange Windows NT client to connect to the server from the same computer on which Microsoft Exchange Server is installed.
6. Try using a different e-mail client. For example, use Microsoft Outlook with the Internet Mail information service in the client profile or use Microsoft Outlook Express.
7. Verify that the Private information store database is consistent and not corrupt. This can cause POP3 login's to fail and POP3 sessions to hang after a command has been issued.

If the problem still occurs, contact the manufacturer of the e-mail client for additional assistance.

For additional information, please see the following articles in the Microsoft Knowledge Base: