Definition
MX (Mail Exchange) records tell the internet which mail servers are responsible for accepting email addressed to your domain. Every domain that sends or receives email must have at least one MX record. Without one, you cannot receive bounces, replies, or FBL reports.
Record Format
yourdomain.com. IN MX 10 mail.yourdomain.com.
yourdomain.com. IN MX 20 backup.yourdomain.com.
- Priority number: Lower numbers are tried first (10 is higher priority than 20)
- Mail server: The hostname of your mail server
- Multiple records: Backup servers provide redundancy if the primary fails
Best Practices
- Have at least two MX records for redundancy
- Set the priority gap wide enough (10, 20, 30) that failover works predictably
- Ensure MX record hostnames have corresponding A records
- Monitor MX record availability as part of your deliverability infrastructure
Common Mistakes
Using CNAME records for MX targets (most standards prohibit this), setting all MX records to the same priority, and forgetting to update MX records after changing ESPs.
Related Glossary Terms
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BIMI
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Bounce Rate Threshold
A bounce rate threshold is the percentage of hard or soft bounces at which email platforms and ISPs begin to penalise sender reputation, typically around 2-5%.
Bounce Rate
Email bounce rate is the percentage of emails that were rejected by the receiving server before reaching the recipient. It is a key indicator of list health and data quality.
Email Deliverability
Email deliverability is the ability to land in the recipient's inbox rather than the spam folder. It depends on sender reputation, authentication, list quality, and content practices.
DKIM (DomainKeys Identified Mail)
DKIM (DomainKeys Identified Mail) is an email authentication method that uses digital signatures to verify that an email was not tampered with during transit and comes from a authorised domain.