Sharing Free/Busy with others not on your server can be a time-saver and Exchange 2010 SP1 makes it easy.
We have a Exchange 2010 Server with calendars that are tied to two conference rooms. We share these conference rooms with another company and they need to see the busy/free information and need to be able to reserve those rooms as well. Can they do this even if they are not part of our network and do not have an Exchange server?
Yes, they can. You need to configure the room calendars so the other company has access to Free/Busy and allow the others to send meetings to the room. They won't need an account on your server to reserve rooms as long as the room is configured to allow outside addresses to create meetings.
You'll use the Set-CalendarProcessing cmdlet to set ProcessExternalMeetingMessages to True so the room processes the meeting requests and will need to enable Internet Calendar publishing on the server.
Set-CalendarProcessing -Identity "conference1" -ProcessExternalMeetingMessages $true
To enable Internet Calendar Publishing, use the following cmdlets to enable calendar sharing on OWA, create a sharing policy then apply it to specific mailboxes or organizational units.
Set-OwaVirtualDirectory -Identity "servername" -ExternalUrl "<URL>" -CalendarPublishingEnabled $true
New-SharingPolicy -Name "InternetCalendar" -Domains 'Anonymous: CalendarSharingFreeBusySimple' -Enabled $true
Set-Mailbox -Identity conference1 -SharingPolicy "InternetCalendar"
You may also want to control how much information is shared and the date ranges to include. The defaults are to share availability only and publish 3 months.
Set-MailboxCalendarFolder -Identity conference1:\Calendar -DetailLevel LimitedDetails -PublishDateRangeTo SixMonths
Enable Internet Calendar Publishing
If you don't use Exchange and have a web server, you can use Outlook's Internet Free/Busy publishing to publish your free/busy. If you need it for internal use only, you can publish Free/Busy to a file server. See Publishing Internet Free/Busy for more information.