You can tell what version of outlook by selecting Help > about this Outlook.

Since you are on an exchange server,Microsfot has the ability to share calenders to all users under the same domain or server account. Since there is no way to updaet one calender to another i would have each user just update the holiday calender only. The calender can be shared to each user within your organization.

I double checked to see if a client side or server rule could be implemented and i had no luck in finding a positive solution.

I hope this helps.