You might have the situation that you are receiving Lync Meeting invites from federated partners using Exchange 2013 and Lync 2013, but when Outlook 2013 or OWA 2013 CU1 brings up the reminder dialog for the meeting, the Join button is missing. Outlook and OWA will show the Join button based on the existence of the MAPI property OnlineMeetingExternalLink on the calendar item representing the meeting in the attendee's mailbox.
It is the Lync Meeting Outlook add-in used by the organizer of the meeting, which sets the property on the meeting invite, before it is sent. However the MAPI property might be stripped from the message, when it is sent from the organizers Exchange 2013 environment to your, i.e. the meeting attendee, Exchange 2013 environment. You need to ensure that in the organizer's Exchange 2013 environment, the remote domain matching your Exchange 2013 environment, has the parameter TNEFEnabled set to True (http://technet.microsoft.com/en-us/library/bb232174.aspx#External). When TNEFEnabled is set to true Exchange 2013 does not strip MAPI properties including OnlineMeetingExternalLink and the Join button will be shown on the reminder.
Let us assume that the SMTP domain of the attendee is contoso.com. In the organizer's Exchange 2013 environment it is necessary to create a remote domain with TNEFEnabled = True representing contoso.com. One way of doing it is by using the following commands in Exchange Management Shell:
Nice post Jens..
After reading through this, I went up to set the property and did it through Shell.
Looks like remote domain management is not possible for now (until CU2) in 2013 through EAC.