I am noticing a number of smtpsvc errors in event log. They are saying couldn't deliver to abc.com domain, the connection was dropped by the remote host. I have seen some discussions that this is due to a possible blacklisting of my email domain, butthe majorityof our emails go through. This is just a small amount of emails that are sent daily that fail. Any ideas?

Are the majority of your e-mails going through to that domain? You might consider enabling the transport logging for your send connector and looking at the event logs when your server attempts to connect to that remote server.

That abc.com is just an example. There are many domains that the smtp server says the same error. They are valid domains as the are contacts for certain employees in the company. I believe that they ae finally making it through as I have not heard from users about emails not making it to destinations. I can try enabling the transport logging and see, I just thought there maybe some obvious things I am not catching. Thanks.