We've added about 20,000 verified email settings for many domains worldwide, so users can instantly get their email settings for IMAP, POP and SMTP by inputing their email address or domain. There's also a JSON API that works like this https://emailsettings.firetrust.com/settings?q=test.user@gma...

So this is basically just reading rfc6186 dns entries/autoconfog.xml/autodiscover.xml and picking the first result right?

No, a bit more reliable - they're actual settings stored from users of one of our products. The next step is to build a system to query newly entered unknown domains.