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>”