How can i validate a message in MS Outlook 2010 using Ready API

There's no functionality I am aware of in ReadyAPI to parse/inspect an email message. If I am wrong, hopefully someone else can chime in. 

Barring that and assuming there is no functionality baked in to ReadyAPI, the only way I can see you doing this is writing a manual test step instructing on saving the file and where to place it. From there, you could either include a manual test step for inspecting the email, or write a groovy script to somehow inspect it. You would have to find or write an applicable script for that, though.