Mailserver autodiscovery doesn't seem to work

[jfly]

This works for @infinisil with his mailserver, but doesn't work with my personal mailserver, nor nixos.org. There's this page about autodiscovery on the SNM guide: https://nixos-mailserver.readthedocs.io/en/latest/autodiscovery.html, but @infinisil says he doesn't have that configured, and things still work in Thunderbird.

We do see some messages from Thunderbird about guessing names, so perhaps there's a mail. naming convention somewhere that we could adopt?

[infinisil]

My theory is that it works on my mailserver because I happen to use mail.infinisil.com subdomain. But in absence of the standard mail. subdomain, the autodiscovery DNS records as described in the link should make it work.