I'm a prospective student at Mac. I'm trying to activate my MAC ID but the only number I have is the student number in my acceptance email. It says: "(found on your Student Acknowledgement email if an applicant or student ID card if current student or for Employees on your Welcome letter)". I've gone through every email possible sent from mcmaster but I can't find this so called" Student Acknoledgement email".

Does anyone know what it is talking about or where I can get this Barcode #?

I was having the exact same problem today.
It's in the application confirmation email. You would've gotten it a while ago.

Phone the registrar's office and the nice person there will sort it out in 5 minutes.