I'm going to be installing and configuring Exchange Server 2003. I have been doing some reading first though as I have no experience in Exchange (and to be honest, Microsofts ideas of logic and intuitiveness leave me shaking my head).
I do however have a lot of experience in Linux/Qmail as well as Unix/Sendmail. Everything thing I read is telling me I will need to install Active Directory. I'm getting a lot of definitions in books of AD but I'm still having a hard time understanding exactly what it is.
So, my question is this: to what in the Unix/Sendmail or Linux/Qmail world does Active directory compare? Is it basically just a hash structure?