Since upgrading from 7 to 8, I'm having issues with email coming in to Nicknames. Unfortunately, it's not every time so that's making it hard for me to locate the root of the problem. Sometimes emails coming in to a nickname will be delivered to the user just fine, and other times the person sending the email in will get a "550 No such recipient". All of our inbound email gets processed through MXLogic, so it's the same hosts and IP's sending to us.

Any suggestions on where I start troubleshooting?