I was going to reply one message to one forum, when I detected that behaviour of different links present in the forum email was pretty different:
1) All the present links (course title, discussion title, message title, show parent and see this in context) redirect me automatically to the login page.
2) BUT the "reply" link send me to one page with "Sorry, guests are not allowed to post. Would you like to log in now with a full user account?". And I'm able to see, in that page, the course name, the forum name and the discussion name.
Not critical but an exposure of information!
Reproduced under 1.8. +1 to fix it on 1.7 if present there too.