554 5.2.0 STOREDRV.Deliver.Exception ... Cannot complete delivery-time processing.

One user in my office cant' receive emails either from the office domain and external domains. The sender will infact receive this error message:

Delivery has failed to these recipients or groups:

user@ourdomain.org
There's a problem with the recipient's mailbox. Please try resending the message. If the problem continues, please contact your helpdesk.

The following organization rejected your message: ourserver.ourdomain.org.

Diagnostic information for administrators:

Generating server: ourserver.ourdomain.org.

user@ourdomain.org
ourserver.ourdomain.org.
Remote Server returned '554 5.2.0 STOREDRV.Deliver.Exception:StoragePermanentException.MapiExceptionDatabaseError; Failed to process message due to a permanent exception with message Cannot complete delivery-time processing.

Additional details:

No attachments were sent with the email. The issue arose after a rollback of our mail server. Retention policies are unchanged from default settings. Email used storage is below 90%. He is the only user of the office to have such issue. The account is not blocked and the mailbox not on Litigation hold.

Through PowerShell I have ran this cmdlet Get-MailboxStatistics user@ourdomain.org | Format-List StorageLimitStatus,TotalItemSize,TotalDeletedItemSize,ItemCount,DeletedItemCount

and found out the following: