What is Mandatory Login?

If needed, you can configure your alumni web site to require that users log into their accounts prior to completing transactions such as membership registration or ticket purchasing. If mandatory login is enabled, alumni, students, and HAA associates must sign in using their HarvardKey usernames and passwords.

Please review page 5 of the Login guide for more details:

If your site does not have  mandatory login, anyone can register for an event.  However, if they use an email address that is already in your database, they will be asked to login.  If they use a unique email address, this will create a new record.  Please check regularly for redundancies.  If an alum creates a guest record while registering for membership – it will create confusion when they try and register for member only events.  Please follow these detailed instructions for the redundancy sniffer to merge records.