Did you know that you can allow users in your Exchange organization to publish their calendars to the Internet so that anyone can view their free/busy availability? Just configure a few settings to get started. To enable an Outlook Web App Virtual Directory and allow calendar publishing,

Set-OWAVirtualDirectory -Identity <Client Access server> -ExternalURL <External URL for Client Access server> -CalendarPublishingEnabled $true

To set the web proxy for the Mailbox server, type:

Set-ExchangeServer -Identity “<Mailbox server>” -InternalWebProxy <webproxy URL>

Finish by setting up a sharing policy for the “Anonymous” Internet domain and assign the sharing policy to a user mailbox. First type:

New-SharingPolicy -Name “<policy name>” -Domains ‘Anonymous: CalendarSharingFreeBusySimple’ -Enabled $True

Then type:

Get-Mailbox -Identity <user alias> | Set-Mailbox -SharingPolicy “<policy name>”