We have an Exchange 2010 server is two CAS servers that is randomly sending NDR's with a 5.7.1. When reviewing the event logs I see an event ID of 4030 with the source of MSExchange Availability and 'replicas for free/busy folder EX:/o=First Organization/ou=Exchange Administrative Group'. When searching this event ID it seems to pertain to environments that have recently had old servers removed after a migration, however, that doesn't seem to be the case in this environment. I have a few questions. Can this event ID cause 5.7.1 NDR's to be randomly sent out when people try to deliver messages to this environment? Or do I need to be searching somewhere else. The event ID 4030 started right at the time users reported senders getting random 5.7.1 NDR's.