Some sentences are more fun to write, or read, than others. For example, here's one of my favorites: "This morning, I had my robot clean the floors." Think about that: For a modest cost, I can get an ACTUAL ROBOT that will do housework. (Sadly, I'm still waiting for my jetpack.) Now let's try another sentence, one that for most readers creates a sensation opposite to the first one: "Hey, what Exchange Server licenses should I buy?"

That's right; it's time for a column about licensing for Microsoft Exchange Server 2010. Bear in mind that I am not a licensing professional. Microsoft actually has legions of people whose job it is to understand and explain the company's licensing policies and requirements. It's possible that everything I say in this column from this point forward will be incorrect, so if you have lingering questions, you should probably go straight to the source. With that said, here are a few things you should know about licensing Exchange 2010.

First, you need one Exchange server license per Exchange server. Let's say you're deploying a two-node database availability group (DAG) with two Hub Transport roles. Put them on two servers, and you need two Exchange server licenses. Split out the Hub Transport roles onto separate machines, and poof! Now you need four server licenses. This condition is also true for the Edge Transport role.

Second, the difference between the Standard and Enterprise server licenses for Exchange is that the Enterprise version gives you more databases. That's it. You get 5 databases per Standard edition server and 100 per Enterprise edition server. Passive database copies count toward the limit.

You don't need the Enterprise edition of Exchange to use DAGs. However, you must have the Enterprise edition of Windows Server 2008 or Windows Server 2008 R2 to create DAGs because DAGs use Windows failover clustering, which is only available in the Windows Server Enterprise edition.

What about client access licenses (CALs)? You need one CAL per user who will connect to Exchange. Although it might not be 100 percent precise, I prefer to think of it as one CAL per mailbox; there are exceptions for users outside your organization, automated tools that use mailboxes, and so on. Exchange doesn't enforce this limit, so it's on you to ensure that you have the correct number of CALs for the set of clients you support.

There are two kinds of CALs: standard and enterprise. The standard CAL provides access to basic Exchange functionality: email, calendaring, contacts, and so forth. You can add enterprise CALs to license some additional features. Read that sentence again: Enterprise CALs are add-ons to the standard CALs. Therefore, if you want to license the enterprise mailbox features for 1000 users, you need 1000 standard CALs and 1000 enterprise CALs.

What does the enterprise CAL buy you? Unified messaging; custom retention policies; advanced Exchange ActiveSync policies; per-user or per-distribution-list journaling; the ability to enable the Personal Archive feature (but more on that in a minute); multi-mailbox search; and what Microsoft calls the "information protection and control" feature set, including transport and Outlook protection rules.

You could also get a variant of the enterprise CAL that includes access to Forefront Online Security for Exchange and grants the right to run Forefront on your local servers. All in all, this CAL is probably the best value if you need any of the other enterprise CAL features.

As for Outlook, it's not included in the CAL for Exchange 2010. You have to buy it separately, and beware that Microsoft now ties specific features to specific license levels of Outlook. For example, Personal Archive access is only available when you buy the volume-license version of Office 2010 Professional Plus. I expect this unwelcome trend to continue; I say "unwelcome" because it makes it harder to select and support the correct version of Outlook or to transition between clients.

Of course, the foregoing only covers Exchange licenses; you also need server licenses and CALs for Windows Server as well as for Lync 2010 and other Microsoft products you choose to integrate with your Exchange environment. Microsoft sells bundles of various CAL options, but I'd need a licensing robot to try to explain how those bundles are configured and priced. Instead, I'll point you to Microsoft's website for the "Microsoft Exchange Server 2010 Licensing" summary and to the Microsoft CAL Suite page for information on the various CAL suite options.

Good luck!

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