Symptoms
Microsoft Exchange Transport doesn't re-encrypt Information Rights Management (IRM)-encrypted messages when it sends them. In the event log, Transport decryption isn't reapplied to the message and you receive a "Microsoft.Exchange.Security.RightsManagement.RightsManagementException: Failed to load icon for the attachment" exception.
Resolution
To fix this issue, install Cumulative Update 13 or a later cumulative update for Exchange Server 2019.
