When attempting to migrate resource mailboxes across via the Exchange 2003 Lotus Notes Connector (Redbull) you may notice that permissions are not migrated correctly. This issue is by design, you will need to set these permissions manually at this time
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Read the complete post at http://blogs.technet.com/caseys/archive/2008/05/07/exchange-2003-redbull-connector-permissions-not-migrated-when-we-migrate-resource-mailboxes.aspx