Block a known spammer

Can you block their IP with your hosting configuration? (nginx, apache, htaccess, etc…)

No…I don’t believe so. I don’t control my own server, but will check with my support guru.

You can work in your own custom validation for the registration process with the wpmem_pre_register_data action. So you could halt registration and return an error based on whatever process you work into your function (be that blocking his email, IP, etc).

Beyond that, there are extensions available to subscribers of the premium support site that include a black list extension. There is also a tutorial and code snippets to describe how to build a honey pot to stop registration spam.