Enterprise Vault Journal - Invalid Journal Report Folder in Outlook

Running EV8 SP4 and Exchange Journaling (Envelope).  Some messages are being sent to the 'Invalid Journal Report' subfolder in Outlook.  The Administrator Guide explains other subfolders (e.g. Failed DL Expansion, Failed to copy, etc.) but not the Invalid Journal Report folder.  What is the purpose of the Invalid Journal Report folder or how does it differ from the other folders?

Thanks in advance,

Tammy