Using C# and .Net (4.0 + ), is there a way to monitor meeting items across all mailboxes in Exchange without having to access each mailbox individually? 

I have to write an integration service that can do this (on Exchange 2010 SP3) and then add all external attendees to a Visitor Management System.

The EWS Managed API and Exchange Management Shell seem to only provide access to a single mailbox's calendar at a time. I've come up with 2 work-around ideas, but neither seem very elegant.
1. Create a Service account that acts as a delegate for all other accounts (This probably has a massive overhead on the System Admin's time, unless it can be done programmatically)

2. Create a Service/resource account that can be added to meetings as a resource. Then create a Outlook plugin that can force the resource on each new meeting created if external addresses are detected. Then hope that the System admins have a way to roll out the Outlook plugin. (Massive overhead on staff, again, but the more elegant of the 2 solutions).

Any help/Ideas will be greatly appreciated. 

• Edited by BeumerE 7 hours 7 minutes ago

Another option would be to use EWS Impersonation. That way you don't have to configure delegation for ever mailbox, but you can access all mailboxes. You still have to access each mailbox individually (there's no getting around that)

Thanks for the Reply, Jason. The more I read up on it and the more examples I see, the more I think that a option 2 is more likely to have success. I may have to negate the plugin idea and trust that meeting organizers will remember to assign the right resources to meetings if they expect external visitors. Using this option also provides a mode of feedback to the meeting organizer, by making the service send a "Tentative" response to the meeting, once all processing is done.

Iterating through a large number of mailboxes is simply not going to cut it, performance wise. My client stated that they have a large number of meetings every day and some are short notice.