I am sensing some pent up anger here - directed via an assumed generalisation at the male species.
Point is, he emailed her and lied about not emailing her. There was a car that the wife saw that he apparently didn't see. Likelihood is that he is cheating, I agree. As long as he continues to lie, he merely digs a deeper hole for himself and makes matters worse for everyone involved.
Women cheat too, and a lot of the time it is driven by emotions as I have yet to meet (in person), a woman driven by her penis! Men have these same/similar emotions and there is no harm hearing his side of the story, unless of course he is a pathological liar. There is no doubting that he has been up to no good - the depth of the **** he is in is questionable and dependant on what he has to say. I am merely pointing out that whilst I disagree wholeheartedly with cheating on your spouse, understanding their reasoning behind it is more beneficial once the reality of the cheating has sunk in.