You were having this problem before and it is inexplicable to me. When I open Windows Live Mail 2012 on my machine and I'm in my inbox message list all I have to do is either TAB to jump to the preview pane to see the message or hit ENTER while on the message to have it open in its own Window.
Reading e-mail as plain text is fine if you want to do so, but it is not necessary for security reasons. Patches to prevent execution of code via HTML e-mail were put into place in contemporary e-mail clients many years ago. This is one of those practices that, while once valuable, is really not so any more.
I can't figure out where you'd even use ALT+M, because that's not a command in the reading side of WLM 2012.
There are commands under ALT+M, the Message Ribbon, when you're replying (or composing a new message), but when I reply I am immediately thrown into the edit box for the message box at the outset and can just type my message. If I am composing a new message I am thrown into the To: field when the window opens up, after filling that in TAB takes me to Subject, and after filling that in TAB takes me to the message body. This is the behavior I've always observed on client computers as well. NVDA just follows right along with where the system cursor has landed each and every time.