These events may be logged for any type unsuccessful authentication, including incorrect password, incorrect username, incorrect password and username combination, or if another session is locking the mailbox. This error may also be logged if you disable the POP3 account.
When the POP3 Connector establishes a session with a POP3 server, it sends the POP3 protocol user command followed by the account name. If the user does not exist, the POP3 server may reply with the -ERR response to the user command. For security reasons, the POP3 server generally sends the +OK response after a user command. If the POP3 Connector receives a +OK response, it sends a pass command together with the password. A successful logon attempt is followed by a +OK response from the POP3 server. If the logon attempt is not successful, the POP3 Connector receives the -ERR response.
The response from a POP3 server to the user and pass commands is only significant to the +OK and -ERR responses. If the POP3 Connector receives a -ERR response, it is unable to determine the reason for the unsucessful authentication and thus reports the errors that you find in the "Symptoms" section in this article.
Some POP3 servers may provide a description string after the -ERR response, for example:
-ERR Incorrect username and/or password.
Anything after +OK or -ERR is specific to the POP3 sever implementation. It is possible to enable the POP3 Connector diagnostic logging to check for a descriptive message after the -ERR response. You may also use Telnet and the POP3 protocol commands to check for the response.
Diagnostic Logging: SBS 4.5
To enable diagnostic logging for the POP3 Connector on SBS 4.5, follow these steps: 1. Click Start, point to Programs, point to Microsoft Exchange, and then click Microsoft Exchange Administrator.
2. In the left pane, expand the Site container, which by default in SBS should be the server name.
3. Expand the Configuration container.
4. Under the Configuration container, click the Connections container.
5. In the right pane, double-click Connector for POP3 Mailboxes to view the properties.
6. On the Diagnostic Logging tab, verify that the Enable event logging on the services check box is selected.
7. Under Category, click Delivery Services.
8. Set SMTP Client Transactions and POP3 Client Transactions to Maximum.
9. Click OK, and then click Yes to restart the POP3 Connector Service.
Diagnostic Logging: SBS 2000
To enable diagnostic logging for the POP3 Connector on SBS 2000, follow these steps: 1. Click Start, point to Programs, point to Microsoft Exchange, and then click System Manager.
2. In the left pane, expand the Connectors node.
3. Right-click Connector for POP3 Mailboxes, and then click Properties.
4. In the Connector for POP3 Mailboxes Properties dialog box, click Diagnostic Logging.
5. Verify that the Enable event logging on the services check box is selected.
6. Under the Services box, click Delivery Service, and under Logging Level click Maximum.
7. Click OK to apply changes.
8. Close the System Manager console.
9. Click Start, point to Programs, point to Administrative Tools, and then click Services.
10. In the left pane, right-click Microsoft Connector for POP3, and then click Restart. After the service restarts, close the Services Management console.
When the POP3 Connector attempts to download messages from the POP3 server it will log a number of events in the Application Log of Event Viewer. You need to wait until the next scheduled download attempt or you can also initiate the download by using the Deliver Now option in the POP3 Connector Properties dialog box. You can then use Event Viewer and search for Event ID 4023, and Source: POP3Connector in the Application Log.
The event 4023 contains the POP3 Protocol transcript between the POP3 server and the POP3 Connector. There should be at least one event 4023 for each individual POP3 mailbox and Global POP3 accounts configured in the POP3 Connector. You will have to view the description of each one until you find the entry that corresponds to the mailbox that is failing.
If you double click on the entry for an event 4023, the description contains the POP3 transcript. You should be able to identify the corresponding account by looking at the entry following the user command. This should be the username for the POP3 account that the POP3 Connector is attempting to access. You should also be able to see the -ERR response after the user command or the pass command. Check if there are any descriptive messages after the -ERR command such as "Access Denied" or "Unable to Lock Mailbox." The transcript should be similar to this sample: C: USER username
S: +OK Password required for user username
C: PASS secret
S: -ERR maildrop already locked
If the mailbox is locked by another session, you need to end that session before accessing the mailbox. Also, verify with your Internet service provider that your username and password are correct and that the POP3 account is enabled.
You should disable diagnostic logging for the POP3 Connector after you have finished troubleshooting. Follow the appropriate method for diagnostic logging earlier in this article and set the logging level back to minimum.
Pls do let me know if this helped.