Are people using web services? If so, do you allow external meeting requests to be sent to your users? I'm following KB20866 because meeting requests from outside users are not being formatted correctly. The fix is easy enough, but it looks like this (setting ProcessExternalMeetingMessages to True on Exchange) is only done at a mailbox level, which means that you have to run the script for every new user you create.

There is no way to set the ProcessExternalMeetingMessages field to true by default. Are others finding a way around this? Is there a better or different approach to take?

EWS is definitely recommended because it's more efficient and reliable than cdo. When setting this up for customers, I always enable external meeting requests. You can enable this by running the shell command or open the user's Exchange profile and enable the option on the Calendar tab. You can just add this as an additional step when creating new mailboxes on Exchange.