Hi Gayle,



The unknown reasons are mainly due to a mail server that initiate a smtp session and terminates the session without either sending anything or stop the smtp session without completing it.



It can also be softwares that tries to test if the smtp port is open.



In summary, in this field is listed all the aborted smtp connection that ended before that the transaction is complete !



On the domino side it's impossible to know what happen !



Hope this helps !



Renaud