A while ago, when commenting on blogs was still a thing, I came up with an ingenious way to solve the spam problem and it worked with 99.9% accuracy. When someone posted a blog comment, I marked it as "pending" and I emailed it to myblogcomments@gmail.com email address. Then a minute later, I connected with POP3 to Gmail and checked the inbox. All spam comments were filtered by Gmail and the good comments ended up in inbox. I then removed the "pending" label and made them visible on my blog.