SMTP Prevent fails to process a message and responds with " 554:Smtp_Message.5300 Error while processing message "
The File reader log shows the following entries
The message has to create fully RFC 2821 (RFC 821) compliant communication with the MTA. See as reference KB 54131
The seen error message is typical when a non-RFC compliant message is encountered. Please review the communication between the MTA and SMTP Prevent.