I'm getting this critical error when I run the Pre-Deployment Analyzer for Exchange 2010: Permissions inheritance block on OU. It says this *may* cause mail flow problems, recipient update service failures, and other service outages. I know how to fix it. What I'm wondering is why is this a problem? Under what circumstances would I experience mailflow problems, recipient update service failures and other service outages? Everything I read about it online is very vague. Can anyone give me a specific scenario under which this might occur?

Its all about permissions. If the inheritance is blocked, then the permissions that Exchange sets for correct operation, with Exchange being able to read and update objects will not work correctly. It is very vague because it is impossible to be specific because the permissions could be very different. It can depend on the account being used, restrictions in place elsewhere etc. Exchange is very heavily integrated to AD, therefore incorrect permissions can cause havoc. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Its all about permissions. If the inheritance is blocked, then the permissions that Exchange sets for correct operation, with Exchange being able to read and update objects will not work correctly. It is very vague because it is impossible to be specific because the permissions could be very different. It can depend on the account being used, restrictions in place elsewhere etc. Exchange is very heavily integrated to AD, therefore incorrect permissions can cause havoc. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.