What is it?
This mail DNS finding means the domain has no MX records. MX records tell other mail servers where to deliver mail for the domain.
Why does it matter?
Without MX records, inbound mail delivery can fail or fall back in inconsistent ways depending on sender behavior. Domains that send mail should also receive important operational mail such as bounces, abuse reports, and DMARC reports.
How to fix it?
Add MX records at the domain apex and point them to hostnames, not IP addresses.
example.com. 3600 IN MX 10 mail.example.com.
mail.example.com. 3600 IN A 203.0.113.20Use multiple MX records only when you actually operate secondary mail exchangers. Make sure each MX hostname has public A or AAAA records and is not a CNAME.