If a classmate has an invalid email address and we have an email that has been bounced back--when this classmate logs on, will they be notified to update their email address?

Yes. Regardless of what email address you have entered for a Classmate, when that Classmate joins they have to enter their current email address. When they see the email address field it will be blank even though you've put something in there for the Classmate. We actually did this for this very reason. It ensures the Classmate will provide a valid email, and removes the possibility of the Classmate leaving an invalid email in place.

Brad,
Sorry I have not been following the instructions. Is there a thread I can read about "bounce back"? I am assuming that when we get the bounce back we should edit that person's profile and delete their email? Or is this done automatically?
thanks

No it is not done automatically. You have to note the reason for the bounce in order to decide what to do next. Maybe somebody's email server was just down for awhile and everything is fine. I.E. no changes are necessary. Or maybe the Classmate's email address is no longer valid, and you really do need to remove it or edit it so it's current. You can only know by seeing the reason for the bounce.

The thread about bouncebacks is here.