Your mailbox is already locked
This error ‘Your mailbox is already locked’ appears while a single mailbox is configured on multiple computers and one session already in progress while another session tries to access the mailbox. When POP3 client establishes the connection with POP3 server it exclusively locks the mailbox for that session.
With Outlook Express
There was a problem logging onto your mail server. Your Password was rejected. Account: ‘Another account’, Server: ‘mail.domain.com’, Protocol: POP3, Server Response: ‘-ERR Your mailbox is already locked‘, Port: 110, Secure(SSL): No, Server Error: 0x800CCC90, Error Number: 0x800CCC92
With Microsoft Office Outlook
Task ‘firstname.lastname@example.org – Receiving’ reported error (0x8004210E) : ‘Your mailbox is temporarily unavailable because another e-mail message is being delivered to it or another mail application is accessing it.Â The server responded: -ERR Your mailbox is already locked‘
Â Troubleshooting the Issue
There is no action needs to be taken from your end. The error will disappear automatically as soon as the mailbox is unlocked by the ongoing POP3 session.