GMS has been configured to manage Delivery Status Notification (DSN) messages. There was no DSN specification with this message so GMS has added it.
In this case session Undefined was receiving a message apparently from Undefined being sent by the machine at Undefined. The DSN details were added to the MAIL clause.
The missing DSN information has been introduced by GMS so no action is required by you. You may like to contact the owner of the domain at Undefined to let them know that their system is not processing DSN requests correctly and suggest they upgrade to a Internet Standard Messaging server like GMS.
What is happening in this case is that either a RET or an ENVID DSN command were given as part of the ESMTP transaction but no parameters were supplied to these commands. As this is an invalid use of DSN GMS has automatically supplied default parameters for the commands as described below.
This is specified on the same line as the MAIL command, and requests that only the headers of the message be returned in any "failed" delivery status notification issued for this recipient.
Again specified in the same line as the MAIL command the UDIL is a unique identifier for the message being sent and should be referenced in any "failed" delivery status notification issued for this recipient.
Keywords:DSN delivery status notification RFC1891 RET ENVID