Introduction

MX priority controls which mail server other systems should try first when delivering mail to your domain. A wrong priority order can route traffic to a backup host, a decommissioned provider, or a server that cannot actually accept mail. The clean fix is to compare your current MX set with the intended provider design and remove any entries that no longer belong in the delivery path.

Symptoms

  • Inbound email is delayed, bouncing, or arriving only intermittently
  • Mail flows to an old provider after a migration
  • The backup mail server receives traffic even during normal operation
  • Validation tools warn about invalid or conflicting MX entries
  • The issue started after moving email providers or editing DNS manually

Common Causes

  • The preferred mail server has a higher numeric priority than the backup server
  • Old MX records were left in place during provider migration
  • An MX target points to a hostname that does not resolve correctly
  • Mixed provider documentation led to duplicate or contradictory entries
  • The domain has one working MX record and another stale record still receiving traffic

Step-by-Step Fix

  1. List every active MX record for the domain, including its priority value and target hostname.
  2. Compare those entries with the exact DNS instructions from the mail provider you intend to use now.
  3. Confirm the lowest numeric priority belongs to the primary mail server and higher values are reserved only for backup paths if required.
  4. Remove obsolete MX targets from previous providers instead of leaving them in place as harmless-looking leftovers.
  5. Verify every MX target hostname resolves to valid mail server addresses and is not set to a bare IP or broken alias.
  6. Check whether the provider expects a single primary MX record or a full set of equal-priority endpoints.
  7. Save the corrected DNS set and allow time for resolver caches to expire before retesting.
  8. Validate inbound mail flow with provider diagnostics and by sending test messages from an external system.
  9. Document the intended mail routing order so future migrations do not leave the domain split across multiple delivery paths.