Default email X-header applied by DLP Network Prevent for Email server and viewable from packet capture.
Modified email X-headers are not viewable from a packet capture and mail is not blocked downstream because of the missing header information.

SMTPPrevent_Operational log errors:
Peer disconnected unexpectedly
Message not accepted by forwarder
4.4.2 service timed out.
disposition=ERROR code=421

RequestProcessor log errors:
com.vontu.mta.rp.ESMTPRequestProcessorThread handleMTAException
java.net.UnknownHostException

Caused by: java.net.UnknownHostException: SERVERNAME: unknown error

at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)

at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:907)

at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1302)

at java.net.InetAddress.getLocalHost(InetAddress.java:1479)

The DLP Network Prevent for Email server failed to resolve it's own hostname through java.net.InetAddress.getLocalHost().

Add the DLP Email Prevent IP and Hostname to /etc/hosts to resolve the issue.
Example: