About the MX Checker
MX (mail exchanger) records tell other servers where to deliver email for your domain. Lower priority numbers are tried first. Each MX must be a host name — not an IP address or a CNAME — and must resolve to a reachable server.
If a domain has no MX record, senders fall back to its A record, which is rarely what you want. Missing or broken MX records are the most common reason a domain stops receiving email.
What are MX records?
MX records tell the world which servers accept email for your domain, in order of priority. They must point to host names (not IPs or CNAMEs) that resolve to public addresses.