When I click on the URL link from email, the following error appears:
No item exists at http://SERVER/SITE/mypage.aspx?ID=1. It may have been deleted or renamed by another user.
This behavior appears while anonymous access is enabled for web application, and the URL link leads to the item where authentication is necessary. So the system is getting conflict and this error is appearing.
Browser tries to access item where anonymous access is forbidden.
As a workaround, you can open your browser on the course page with logged account. In that case browser will open the link with enough permissions.