We are runing Exchange 2010 SP3 w/Update Rollup 2 on two MB servers and 2 HT/CAS servers. We have several application servers that route emails through Exchange and a couple of them have had issues with what appeared to be a delay in closing after sending an email. During testing, we found that when the app is opened and email is sent, we can see the email getting delivered to the user's Outlook, but the application remains open for about 30 seconds or more. I adjusted the -maxacknowledgementdelay to 5 seconds on the receive connectors and that "fixed" the issue for 2 of the applications. The third one still does the same thing. Once an email is sent, we can see that it is delivered to the user, but the application remains open for about a minute. I changed the -maxacknowledgementdelay on this app's receive connector to 0, restarted the Transport service on both HT/CAS servers, but it still takes about a minute to close the app. I am at a loss to understand why this one is not working as the others. Any help is appreciated.