Ahh, so is it a one time fee of X per Y users. For example, say I was running trekbbs and for email I was using exchange as the server and wanted to set up 10 email addresses under the same trekbbs domain. Is it something like a one time charge of $50 per each address on that domain?
Yep you simply pay for the CALS which allow X number of users to connect (minimum is 5) and that would allow 5 users to connect to Exchange Server at the same (including through outlook web agent).
You can have 30 users, each with with 1 or 10 e-mail addresses but if you've only got 10 CALS then only 10 users can connect at once.
Let's say you're running a Call Centre. You have 30 staff rotated over 3 shifts. You're never going to have 30 people connected at once so why pay for 30 licences. Instead you create mail accounts for the 30 users and the however many e-mail addresses they have but have 10 CALS. So when each shift finishes the users logoff and the next batch logs on.
furher a realword example I did for a client.
They had .com.au tied to the firm name but the firm changed names and was getting a new domain.
The new name was registered/delegated/pointed to their IP address. During the change over both names would be used because a lot of e-mail would still be coming using the old address.
Running Small Business Server 2003, 25 Client Access Licences.
I set Exchange to receive e-mail domain1.com.au and domain2.com. Each user had e-mail addresses of <name>@domain1.com.au and <name>@domain2.com.au so effectively 40 odd e-mail address. Additonal licences requried - zilch because it was still only 20 users connecting.
And on the subject of Exchange Server, if you're looking to setup it, explore the option of Small Business Server 2008 and you can't go wrong. It gives your Windows Server and Exchange Server CALS in one bundle and is far far cheaper than buy Windows Server + CALS and Exchange Server + CALS.
One point - SBS used to include Outlook but that's not the case anymore.
If you're in a book store, take at look at SAMS Small Business Server 2008 Unleashed (couple of ommission relating to the Printers and the fax services) but it's a pretty good book (should be able to pick it up for under $50 on Amazon)