Blog article
- 8 minutes read
- Kiara Saloojee
- DMARC Enthusiast
MX Record: The DNS Entry Behind Every Email You Receive
MX record overview:
- MX records direct inbound email to the correct server
- Priority values determine which server receives an email
- Misconfigured or outdated records create both delivery and security risks
- Continuous monitoring is the only reliable way to catch DNS changes before they cause damage
Every email sent to your domain has to find its way to the right server. DNS MX records make that possible. For teams managing enterprise email environments, understanding how MX records work – and what breaks when they don’t – is foundational to both delivery and security.
Sendmarc monitors your email authentication environment – so misconfigurations don’t go undetected. See the platform in action.
Understanding an MX Record
An MX record is a DNS record that tells sending servers where to deliver email. When someone sends an email to [email protected], the sending server queries DNS to find the MX record. That record points to the hostname of the server that should receive the message.
MX records don’t store IP addresses. They store hostnames instead – like mail.yourdomain.com – and the DNS resolves those using A or AAAA records.
How MX Records Work
The process runs in the background during every email delivery:
- The sender’s server queries the DNS for the MX record
- The DNS returns the MX record, which includes a hostname and a priority value
- The sending server connects to that hostname over SMTP (port 25) and delivers the message
This lookup happens before any message content is exchanged. If the DNS can’t return a valid MX record, delivery can be unreliable.
Understanding MX Record Priority
Each MX record includes a priority value – a number that tells sending servers which server to try first. Lower numbers mean higher priority.
For example:
| Type | Host | Server | Priority | TTL |
|---|---|---|---|---|
MX | domain.com | [email protected] | 10 | 3600 |
This record directs any server sending email to domain.com to deliver the message to mail.domain.com. The priority value of 10 determines delivery order. The TTL of 3,600 seconds tells DNS resolvers to cache the record for one hour.
When two records share the same priority, sending servers distribute delivery between them.
Multiple MX Records and Redundancy
Enterprises rarely rely on a single MX record. Configuring multiple records creates redundancy. If the primary server is down, delivery automatically routes to the backup.
This failover behavior is handled entirely by the DNS – no manual intervention is required. However, it only works if all MX records are correctly configured and actively monitored. A stale or broken backup record can introduce unpredictable delivery behavior.
For organizations managing large, distributed environments, this means MX record hygiene is an ongoing operation.
What Happens When MX Records Are Misconfigured
MX record errors fall into two categories: Delivery failures and security gaps.
Delivery failures occur when:
- The MX record points to a hostname that doesn’t exist
- Priority values are misconfigured, routing traffic to an unavailable server
- Records haven’t been updated after a server migration
When MX records are broken, critical communications – billing, notifications, transactional emails – don’t reach their destination. In enterprise environments, diagnosing these failures is time-consuming without centralized visibility into DNS configurations.
Security gaps occur when:
- Outdated MX records point to decommissioned infrastructure that an attacker could re-register
- MX records haven’t been audited, leaving gaps that expose the domain to spoofing and phishing attacks
These issues are hard to detect without continuous monitoring. Manual investigation of suspicious email failures and DNS inconsistencies adds operational burden to stretched security and IT teams.
Best Practices for MX Record Management
1. Use at Least Two MX Records
Configure a primary and at least one backup with a higher priority value. This ensures continuity if the primary server is unavailable.
2. Point MX Records to Hostnames
DNS requires MX records to reference a hostname. Pointing directly to an IP address isn’t valid and will cause delivery failures.
3. Keep Records Current
Update MX records immediately after migrating email infrastructure. Stale records pointing to old servers are a delivery and security risk.
4. Monitor Continuously
DNS changes – including unauthorized ones – can go undetected for days or weeks. Continuous monitoring of MX, SPF, DKIM, and DMARC records provides the visibility needed to catch misconfigurations before they affect delivery or security.
Where Sendmarc Comes In
MX records are simple in concept but consequential in practice. A single misconfiguration can break email delivery or expose your domain to exploitation. In distributed enterprise environments, maintaining accurate, monitored DNS records across all domains and sending sources is an ongoing task.
Teams that treat DNS management as a core part of their security are better positioned to protect email delivery and enforce authentication at scale.
Sendmarc provides continuous monitoring and management of DMARC, SPF, DKIM, and DNS configurations across enterprise environments. Learn how Sendmarc works.