One tip - remove the standard text that is displayed for mini guest post forums, e.g. "You are welcome to post anonymously by entering a nickname" etc etc... Spammers simply search for keywords like this and you're easy meat - they know they don't have to register to post.
Thanks for the tip; but as you see, you were posting as Guest. Not every board has this greatest feature enabled, and visitors should now about it. That could force them to create new, unique posts. If you protect the board by the Captcha add-on
, it doesn't matter if spammers find your board or not - they won't be able to automate their devil anyway.
Also, spammers most likely are about posting hyperlinks. Guests in miniBB are not allowed to post hyperlinks. I guess, that may reduce the spamming amount, too. I think spammers already "know" about that feature, so even on our board, we do not experience even manual spam from guests. It's not just worth it.
So I think, we will hold your suggestion by now. We must care about regular visitors, not spammers :)