An event sink is best described as a sub-routine that is keyed to run at specific points in the message flow. Usually there are two places that an event sink ties in. One is just before the categorizer and the other is just after. However, there are also sinks that run during message transfer. A very typical event sink is anti-virus products. Just prior to submission to the categorizer, it sends the message to the AV product where it's scanned and then returned to the routing process. In the past I've seen sinks for some products that will attempt to verify a name in the GAL prior to sending a message and it would do this on the message submission to the remote domain. The problem that I saw was where the message would begin transfer and then drop the connection part way through. What had happened was the customer had installed and the uninstalled a demo version of a product. It had removed the files for the event sink, but not the sink itself. When we tried to send to the other domain, it would get about halfway through and then drop the connection when the sink tried to fire and the files were missing. But than again, I've this error when mail was being sent out from one of our sites directly out to the internet rather then routing our HQ. Therefore; this was caused by reverse dns lookups failing for mail that was routing out the site and would product the error The connection was dropped due to an SMTP protocol event sink. Possible there was some application the remote party was running on top of Exchange that was doing some validation. ________________________________ From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Andrew English Sent: Wednesday, May 17, 2006 12:45 PM To: exchangelist@xxxxxxxxxxxxx Subject: [ExchangeList] Re: SMTP Error?? What does this mean? "The connection was dropped due to an SMTP protocol even sink." ?? Regards, Andrew