It's a wonderful project. There's something romantic about it, for sure.
And if I could plug my own project, you could also do it by just sending emails: https://publicemails.com.
And if I could plug my own project, you could also do it by just sending emails: https://publicemails.com.
You could also do some heuristics like not accepting emails with excessive HTML. Though I'm not sure how much it'd work, since you already require confirmation so presumably the spammers actually have someone authorizing the publication. (I didn't test your flow since I have nothing that warrants posting to say)