3. If BOFHCHECKDNS option is on, courieresmtpd rejects mail from some valid
domains (e.g. mz.ru, tech.ru, games.dol.ru, home.com, exite.com,
maxmail.co.uk) with diagnostic "Domain does not exist". It's caused by
misinterpreting error responses from MX list creation functions. I think
this diagnostic should only appear if DNS replies with NXDOMAIN status.
Right. Which is exactly the case here.
mz.ru. 14400 IN MX 20 delta.4markets.ru.
mz.ru. 14400 IN MX 10 delta.4markets.ru.