Google’s built in spam protection in their Gmail system is very good. However, some messages manage to get through and clicking ‘Report Spam’ removes it from your inbox but does not necessarily prevent future messages from the sender. The solution is using a blacklist, but unfortunately this is not immediately offered by Gmail.

The solution is just to create your own blacklist using a filter. The linked article walks you through the process of blacklisting some existing contacts you may have, however ongoing you will need to update the list manually. Hopefully, these emails are few and far between so adding a new email to your blacklist is not done very often.