Soudless,
Thanks for your compliments.
Well, I wouldn't suggest you to submit or base your interview discussion on email conversation. First reason is that email communication/conversation isn't a standard legal/official document, though emails are accepted by the employers as a proof of employee's job functions. The second reason is that there might exist certain sentence/information which you might overlook but VO could catch it which might effect your application negatively. But if you have other official document such as offer letter, contract with job description that will obviously support your reference letter as these are standard official documents and there shouldn't be any sentence/information existing in such document which could harm your case.
I believe that if you have ONLY a reference letter from your HR/Line Manager on proper company letterhead with detailed job description and you can discuss & explain your job description in details during interview, that would suffice and VO officer will understand that you are genuine.
Off course, this is my understanding & point of view, you are free to decide and act.