Well, yeah of course the developer says "as far as he knows" it's compatible. I could have told you he'd say that. What I want to know is whether or not it actually is. Maybe an Admin tested it?
Personally, I tested it and it seems to work. When I viewed the Full Header it sent and compared it to the actual full header (from the web based mail client, not Outlook's); it was only missing one or two lines (didn't seem like important ones though). And it's probably Outlook that stripped these lines. Also, there was a couple extra ones, but those were just X-headers from my Avira security software.