I hope u are having an exchange and a windows domain.Create three user objects in the name of three conference rooms. Make it mail enabled.Login to each of these accounts through outlookOpen - Outlook Tools -> Options -> Calendar Options -> Resource Scheduling Use these three options: Automatically accept meeting requests and cancellations. Automatically decline conflicting meeting requests. Automatically decline recurring meeting requests. Make the administrator account having full privilage in this tab so that u guys can delete or modify the meetings if needed.On more option is there. but more complicated.Both are described in sourse link.Cheers!Shaba
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