We have two companies in the same forest, but different domains. When we had both companies on Exchange 2003, calendars could be viewed by all across the domains. Now that there is a new Exchange 2007 server and one company migrated, we cannot see the calendars of those Exchange 2007 users anymore.I think its a firewall issue, but which port would be required?

Hello,It is supposed to be permission issue and not firewall. How did you configure calendar sharing on Exchange 2003 servers earlier?Just check a test user by giving Default Reviewer permission on calendar, if you can see then check below article to share calendar of all users available on Exchange 2007 server across the organization.FAQ: Give Calendar Read Permission on all Mailboxes - PFDavAdminhttp://exchangeshare.wordpress.com/2008/05/27/faq-give-calendar-read-permission-on-all-mailboxes-pfdavadmin/Amit Tank | MVP - Exchange | MCITP:EMA MCSA:M | http://ExchangeShare.WordPress.com