UBE messages often use invalid originator addresses. The Messaging Server SMTP server can take advantage of this by reflecting messages with invalid originator addresses. If the originator's address does not correspond to a valid host name, as determined by a query to the DNS server, the message can be rejected. Note that a potential performance penalty can be incurred with such use of the DNS.
You enable address verification on a per-channel basis with the mailfromdnsverify channel keyword described in the Sun Java System Messaging Server 6.3 Administration Guide.