If you configure phpBB so that the first X posts have to be approved by a mod, editing a post (when the user has less than X posts) also has to be approved. This is IMO a good way to make spamming harder. And as phpBB is open-source, you can always modify the source to code your own restrictions.
You could perhaps code it so that links containing certain words are automatically converted to links to a Mint webpage. By looking through spam messages, you can collect lots of words for this. (And you can, if you have time to code it, do this only for people with less than X posts)
Registered Linux User #528502
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