Recently in Apple's Mail app one (subscribed) daily email does not allow scrolling. To read it in full I have to make a pdf. Just this one email source, and not always, never on iPhone. Curious and curiouser :))
I have had the same problem. Also a similar problem very occasionally with the AUGW newsletter which only shows the first part of it contents.
Many such messages (including AUGW) are actually created in HTML, like a mini web page. I suspect an issue with Mail's rendering (decoding) of HTML though it could be that Mail is just not as lenient with HTML errors as some browsers.
There may also be some subtle bugs elsewhere: I had one recently where trying to scroll with the mouse was more successful than with the trackpad!