Figure out which Exchange development technology is right for you

The Exchange 2003 SDK has a list of the technologies
and information about each one (examples of when you would want to use it, whether
or not it's managed, required permissions, etc). This is a nice high-level overview
to help focus you decide which technology is appropriate for your needs:

https://msdn.microsoft.com/library/default.asp?url=/library/en-us/e2k3/e2k3/_techsel_bytechnology.asp