On more than a few projects, I have ended up using
Gravity Forms either because it was previously installed or was the need of the hour based on the requirements.
Recently, I was asked to ban a certain email address due to frequent spamming by the email address in concern. I am aware of the fact that the spammer can change email address and continue spamming. My task was simple, just ban the email address.
Here is how I chose to complete the task