MX records explained: priority, examples, lookup, and fixes
Learn what MX records do, how priority and fallback work, which DNS mistakes break inbound mail, and how to verify MX routing safely.
MX (Mail Exchanger) records are the most consequential 50 bytes of DNS most people never check. They tell every sending server in the world where to deliver mail addressed to your domain — and a single typo can route weeks of important messages into a black hole. Use domain monitoring or deliverability testing when MX, SPF, DKIM, DMARC, or reply routing must be verified together.
Anatomy of an MX record
| Host | Type | Value | TTL |
|---|---|---|---|
| example.com | MX | 1 smtp.google.com | 3600 |
The 1 is the priority. Lower numbers win. Google Workspace has consolidated to a single MX, but historical setups often have 5-10 records with priorities like 10, 20, 30 etc. Sending servers try the lowest first, then fall back if it's unreachable.
Multi-MX with priority
| Host | Type | Value | TTL |
|---|---|---|---|
| example.com | MX | 0 example-com.mail.protection.outlook.com | 3600 |
| example.com | MX | 10 backup-mx.example.com | 3600 |
Common mistakes
| Mistake | Likely impact | Fix |
|---|---|---|
| MX points to a CNAME | Some senders reject or fail lookup | Point MX directly at a hostname with A/AAAA |
| MX points to an IP address | Invalid MX target | Create a named host and point MX to it |
| Old backup MX still live | Spam or intermittent delivery through stale host | Remove it unless it is fully maintained |
| No MX on a sending domain | Some filters treat the domain as suspicious | Publish a real MX or explicit null MX |
- MX pointing to a CNAME. RFC violation. Most receivers handle it but some throw 5xx. Always point MX to an A/AAAA record.
- MX pointing to an IP. Same problem — must be a hostname.
- Same priority on every record. Allowed, but means random selection. Use distinct priorities unless you genuinely want round-robin.
- TTL too long. 86400 (1 day) means a typo takes a day to roll back. 3600 is friendlier.
- Missing trailing dot. In some DNS interfaces,
smtp.google.comwithout a trailing dot becomessmtp.google.com.example.com. Disaster.
Verifying your MX
For a browser-based check, use the free MX lookup. It shows the currently published exchanges and priorities without SMTP mailbox probing or retaining the submitted domain.
# dig
dig +short MX example.com
# host
host -t MX example.com
# nslookup
nslookup -type=mx example.comFrequently asked questions
Last updated May 24, 2026.
Sources reviewed
- RFC 7505: Null MX(standard)
Factual review: June 13, 2026 by WillItInbox Editorial.
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