Many are still confused about the licensing around the Exchange hybrid server required for co-existing with Office 365.
Hybrid server is not a “special” version of Exchange, but one with CAS and Hub roles in the case of Exchange 2010 and CAS and Mailbox role in the case of 2013. You are not allowed to host any mailboxes on this server. It’s only job is to be the middle man in a hybrid deployment of Office 365.
Now the main confusion is around licensing and obtaining license keys. If you have an Exchange deployment on-premise already and want to move/co-exist with O365, you need one or more Exchange 2010 SP3 or 2013 “hybrid” servers.
If the on-premise deployment is Exchange 2003, you can only use Exchange 2010 SP3 servers as hybrid (no 2013). Any deployment with Exchange 2007+ can and should (for the updated feature set) use Exchange 2013 SP1 as the hybrid server. Of course, the 2010 SP3 hybrid servers support all on-premise deployments with Exchange 2003 SP2 or higher.
If the on-premise deployment is Exchange, you can obtain the hybrid server keys for free by contacting the O365 support team. Microsoft has made it easy and you can request and obtain the hybrid key, all online – from here.
Login to the portal and request for the key.
You need to be a paying Office 365 customer though (Enterprise & no trials).
You will be notified if you are not eligible for the free hybrid keys – either because you don’t have an enterprise plan or you are a trial user.
If you need more than one hybrid servers (which you should for redundancy), you can use the same key on multiple servers.
Hope this clears the confusing around licensing hybrid servers. In short, it’s free if you are a paying enterprise customer! ;)