Exchange Server Hybrid Edition key

Organizations that install an Exchange 2010 server solely to act as a bridge between their Exchange Server 2003 or Exchange Server 2007 on-premises environments and Exchange Online can request a Hybrid Edition server key to license the server (or to license multiple servers for redundancy purposes). The Hybrid Edition server key is provided at no cost. Organizations can obtain a Hybrid Edition server key by contacting Office 365 support, who will verify that the organization has a valid Exchange Online subscription and then send the key via email. The Hybrid Edition key is not available to trial customers.
The Hybrid Edition server cannot be used for other purposes besides connecting the legacy Exchange Server environment to the cloud. If the organization moves a mailbox to the Exchange 2010 server, or takes advantage of any other Exchange Server 2010 feature outside of the scope of the hybrid deployment, a regular Exchange Server 2010 license and Exchange Server 2010 CALs are required.