Lync Room System relies on the Join Lync Meeting link in the calendar meeting request. The join link is usually found in the body of a meeting request. However, LRS depends on this link to be present in the MAPI properties of the message. When this meeting request is sent to remote organizations (Lync federated partners), by default the remote organization’s LRS will not show the meeting join link on the calendar. In fact, any Outlook users in the remote organization will be unable to join the Lync meeting with a right click of the calendar item or from within the meeting reminder. They must open meeting invite and click Join Lync Meeting in the body of the message.
The reason for this limitation is that Outlook and Microsoft Exchange do not use a special method to package information for sending messages across the Internet. This method, referred to as Transport Neutral Encapsulation Format (TNEF), is disabled by default for messages sent externally from an Exchange organization. For a meeting join link to appear on a remote LRS, the sending organization must enable TNEF by using the following cmdlet:
New-RemoteDomain -DomainName Contoso.com -Name Contoso
Set-RemoteDomain -Identity Contoso -TNEFEnabled $true
After TNEF is enabled for the remote organization, any message sent over the Internet to the organization is sent as an attachment in TNEF format. With TNEF enabled, when a Lync meeting request is sent to the Lync federated partner, LRS will be able to render the Join Lync Meeting and remote users will be able to join Lync meetings.