POP3 mail client aborts email collection with the following error message: '-ERR Lock Exists. Is another session active??.' 

SYMPTOMS
A single user will not be able to collect mail from CMail using a POP3 mail client while other users collect mail without a problem. The POP3 mail client will report a '-ERR Lock Exists. Is another session active??.' error message.

CAUSE
When a user logs in to collect POP3 mail, CMail creates a Lock file. This means that the mailbox becomes read only until the user is finished collecting mail from the server. Mailbox locking is done to stop the server placing more mail in the users inbox while a collection is in progress and therefore prevent data conflicts and corruption. If CMail is restarted in the middle of a POP3 collection, the connection from the client is terminated abnormally or another user tries to collect from the same box while a collection is active, the user will receive the Lock Exists error message. 

RESOLUTION
The Lock file can be deleted to free the mailbox. This is done by opening Windows Explorer, locating the locked users home directory usually located in the CMail\Spool\username directory and removing any files with a .pop extension.

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