Well, @codinghorror can weigh in here (as he’s who’ll accept the PR should I submit it), but that DIRE WARNING applies to the people for whom discourse-setup is designed. Most of those people cannot and should not be configuring a no-password mail server on port 25; that’s a bad idea except in situations few people are likely to encounter. The likelihood that someone who tries to configure mail that way will then come here asking why, oh why, is their mail not getting delivered is fairly high. Again, if you know how to run a mail server, then you can know that the DIRE WARNING does not apply to you.