reset all users exchange calendar permissions

I need to reset the "Default" permission on all users calendars to be Reviewer.  I can do this user by user in PS using the "set-MailboxFolderPermission <mailbox>:\Calendar –User default –AccessRights Reviewer" cmd but I want to do this for 200 users (everyone who has a mailbox in exchange.

I can list all users in a given database "get-mailbox -database <databasename>" but I don't know how to then use this output to then set the permission.

I am using exchange2010 with server 2008r2

Any assistance will be great thanks.