I was just wondering, if i send someone with mcmaster email address a message using an email that's not my mcmaster email. Wouldn't that person be able to receive it?
I'm just asking, because i remember that in the summer, i was told that for course changing we aren't suppose to send message anything other than our mcmaster email. So was this that they would receive it and not read it, or just not at all being able to receive it

It depends, generally administration and profs prefer receiving emails from mcmaster addresses just to help filter out the random spam from non-students etc. Some profs I know of and admin actually have an email filter set up that auto-removes non-mcmaster-address emails too though.

Either way, it's always best to send your emails via your mcmaster-email if it's to a prof or university administration.

If you send an email to any @mcmaster.ca address from a non-McMaster email address (@gmail.com, @hotmail.com etc.) the recipient will receive it.

Some professors prefer to communicate with students only through the McMaster email, simply because of preference and it proves your a student in their class since your address includes your mac id.

Yeah, they generally don't accept anything other than a McMaster email address because they need to have some sort of proof that you are who you say you are (just having someone's MacID and/or student number doesn't accomplish this since those aren't really all that secret), as well as have a way of filtering out spam. The email will physically go through though. If you want to test it, you can just send an email to your Mac account from your non-Mac account (hotmail, gmail, etc).