It is not clear to students that a reply to an announcement email will be visible to the whole class, so my goal is to make it impossible for students to post replies to announcements.

I created a test site today, and disabled comments on announcements in the Settings > "More Options" section. Then, I created an announcement.  I received the email in my external client and replied with a message, but the reply showed up in canvas.  

Questions:

My expectation would be that disabling comments would disable all comments.  In this case, it would be helpful to understand why it isn't working that way: is this happening because I, as a Teacher, replied to my own announcement? What would happen if a Student replied to the email? 

Is there any way to completely disable replies to announcements?