OpManager REST API

Hello,

I'm new to API's and trying to get a simple "GetMailServerSettings" query to work. I've done lots of searching, but can't seem to figure it out. Here's the HTTP GET query I'm using:

"http://opmanserver:8060/api/GetMailServerSettings?apiKey=c3dd12f549f8afadsfaf2082bb5643d315"

I have tried all sorts of variations...
Can anybody help me build the correct string?

Thank you,
Max