tmda.netは安全ですか？

I agree with blazluin. Challenge-response blocks spam highly effectively. If someone hates this site, you can almost count on them being spammers. Granted, challenge-response has pros and cons but good configuration, a good firewall, and a good starting whitelist and blacklist and good MTA server configuration to block the obvious spam attacks can do wonders. Add to this something like SpamAssassin to filter the unknown emails and knock out the Viagras and bogus watches, collect IP's of spammers for the firewall, and then let the unknowns that make it this far go into TMDA or BoxTrapper or some kind of challenge-response system, and your email system will run free and easy, and those idiots who circumvent the filters will have no hope of getting through unless they go to the trouble of writing code to send back a response. Then just add captcha and their hard work goes for naught. Collect up their spam for evidence. Hand it over to ***** and to their ISP's and to the owners of routers that route their traffic. Find out if you can get them sued or get the companies that support them sued. If possible, draw and quarter them and burn them at the stake if your in the mood to be kind to them.