Does having an "alternate email address" in my profile cause CSS emails to go to that address?

Not really.

For simplicity, most CSS email communications will be sent to your "@columbiasecondary.org" account. Having an alternate email address in your web portal profile will not cause email to be forwarded to that account.

To accomplish this, you must go to your webmail account and set up email forwarding. Learn how to do this here.