Since the last few days I have been receiving more newsletter subscriptions than usual. The emails and frequency look suspicious. Like every hour or two. I tested one of the emails with cleantalk and I got:
email@example.com reported as spam 42 websites attacked, discovered Oct 14, 2019, last activity Oct 14, 2019 23:26:38.
I don't understand the goal of those subscriptions? Why would they be useful to a spammer? Is there a risk keeping them in my database except having bounces?
How to prevent these spam? I have a CSRF protection on the form, it doesn't seem enough. Thanks.