Softonic

MX Record Lookup

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When email bounces, the first place to look is the recipient’s MX records. This lookup queries authoritative DNS for any domain and returns the full list of mail exchanger hostnames, their priority values and resolved IPs, the same picture a sending SMTP server would see before trying to deliver.

How the MX lookup works

  1. 1

    Enter the domain

    Type the apex domain, for example example.com. Do not include "mail." or a protocol.

  2. 2

    Query DNS

    The tool asks public resolvers for the MX record set and reads back each entry.

  3. 3

    See priorities

    Lower priority numbers are tried first. Equal priorities are load-balanced in round-robin.

  4. 4

    Resolve hostnames

    Each MX target is resolved to an A or AAAA record so you can spot dead hosts.

What MX records actually do

MX (Mail Exchanger) records tell the world which servers accept email for a given domain. They are returned in response to a DNS query of type MX and each entry has two parts: a priority number and a hostname. Sending servers try the lowest priority first, then fall back on higher numbers if delivery fails.

Anatomy of an MX record

Field Example Meaning
Priority 10 Preference order, lower wins
Exchanger aspmx.l.google.com. Hostname of the receiving mail server
TTL 3600 Seconds a resolver may cache the answer

Common mistakes this lookup catches

  • A record instead of MX. Some domains accidentally point the apex at a webmail host rather than setting MX records, and delivery silently fails.
  • CNAME at the apex. MX targets must be hostnames with A/AAAA records. A CNAME as an MX target violates RFC 2181.
  • Missing null MX. If a domain does not receive email, publish MX 0 . so senders bounce fast instead of retrying for days.
  • Stale Google or Microsoft targets. Tenants migrating to Microsoft 365 often forget to drop old aspmx.l.google.com entries.

Frequently Asked Questions

Redundancy. Email is store-and-forward, so providers list multiple mail exchangers at different priorities. If the primary goes down, senders try the next priority automatically.

It is the highest preference, tried first. The actual number matters only relative to other records in the same set. A single MX at priority 10 behaves identically to one at priority 0.

Technically yes. In that case senders fall back to the A record, but modern providers often refuse to deliver in that situation. If a domain does not accept mail, publish a null MX instead.

DNS caches. Different resolvers may hold stale records until the TTL expires. If you just changed your MX, wait for the old TTL to pass before comparing.

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