We are running one MS Exchange 2010 on Server 2008 R2, virtualized through hyper-v, no SP on either.
We seem to have remnants of the old 2003 exchange hanging in there somewhere. We are experiencing our second round of fighting an issue where emails are delayed sometimes over 20 minutes. You will not receive anything, then after a random amount of time, ten emails will drop into your inbox. I had one email that I never received, but an hour later I got a reply to that email, than an hour after that I received the original email. There are no events or helpful clues to go by.