#554-5.2.1 mailbox disabled 554 5.2.1 STOREDRV.Deliver.Exception:AccountDisabledException.MapiExceptionMailboxDisabled; Failed to process message due to a permanent exception with message Cannot open mailbox /o=First Organization/ou=Exchange Administrative Group.
I checked into Active directory users are not disabled, so i tried with log on to OWA (webmail) but still getting same error that your mailbox is disabled. i noticed that all these users are on same database of Exchange Server.
Run the following cmdlet on Exchange PowerShell:
After running avobe command issue got resolved permanently.