WordPress Membership Plugin
Not only tables filing up, but also the mail system tries to sent out emails to these bogus accounts as well. These get stuck in www-mail account, which builds up as well and because of all the bad mail, lowers your mail reputation score with the large providers such as Gmail.
Each time is a different IP & email combination, so whitelist/blacklist is not a solution.
I wish I could charge a fee for but, but unfortunately cannot.
If these are indeed coming from a Bot, how is it getting past Captcha v3
There has to be a better solution to the issue.