@adorfer, about how many blacklisted emails are you seeing in new user accounts per month?
Since such a plugin would require a database of blacklisted emails that’s hosted externally and maintained, would you be willing to pay a small monthly fee for such a service? If so, what would be a reasonable price to pay?
i guess should work like a DNS-RBL-Check:
at least one for “IP is VPN-Exit”, one “IP is Tor exit”, one “fqdn is oneoff-mailer”.
Combining those results may already lead to a good evaualuation e.g. to put a user into “team validation”.
That’s a bit beyond what I had in mind, but I guess it could work if you had a good source for IPs.
My idea was to just maintain a database of free email service domains (and possibly domains created solely for spamming) and then auto delete/silence users who join with one of those email addresses. There would be no need to put those new users into “team validation” since the domains are already known to be problematic.
For reference/calibration, we have installed a blacklist of ~4500 domains and it seems stable. We are on Discourse Hosting Standard Plan. 