For what it’s worth, I have a vague recollection that some Catholic high schools provide student email addresses for their Catholic students only to various Catholic universities. I don’t know where I read that, though. That might explain your friend receiving emails while you did not, especially since it sounds like your friend’s emails were not due to listing ND on the Common App.
BC does not discriminate on the basis of religion http://www.bc.edu/offices/diversity/compliance/nondiscrim.html
and “welcomes all faith traditions and encourages students to explore their spirituality and engage in discussions of faith-based issues.” http://www.bc.edu/bc-web/jesuit-catholic.html#par-bc_tabbed_content-tab-1
I suggest you hunt around ND’s website for similar information.