My email is LOCKED! Please help!

My email is LOCKED! Please help!

Task ' info@NorthernColoradoRentals.com - 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.  The server responded: -ERR Mailbox locked.'

I've turned off all other devices accessing this account, but I continue to get this error message.  Is there a way you can UNLOCK the mailbox?