After you've registered on SOLAR, wait 24 hours and then go to MUGSI > My MUGSI > Quick Links > Enable your MAC ID Services
You can only access your Mac email account after you do this step of activating MAC ID services (not the same as activating your MAC ID, which allowed you to get onto MUGSI/SOLAR)
The login for email is here:
https://muss.cis.mcmaster.ca/
Also your email account won't receive messages from other servers (e.g., Gmail) immediately, this apparently takes a while too (48 hours?)