MX Lookup - Mail Server Record Analysis

An MX lookup queries a domain's mail exchange records to discover which servers handle its email. Use robtex.com to retrieve all MX records with priorities, helping troubleshoot email delivery and verify mail infrastructure configuration.

Understanding MX Records

Mail exchange (MX) records tell sending servers where to deliver email. When you send to user@example.com, the sending server queries example.com's MX records to find receiving mail servers.

MX records contain:

  • Priority (preference) - Lower numbers are tried first
  • Mail server hostname - The receiving server's address
  • Resolved IP - Where that hostname points (via A record lookup)

How Mail Routing Works

Sending servers query MX records, then attempt delivery to the lowest-priority server first. If that server is unavailable, they try higher-priority servers as fallbacks.

Common configurations:

Single server - Small domains often have one MX record pointing to their hosting provider.

Primary/backup - Two or more servers with different priorities. The primary handles normal traffic; backups queue mail if primary fails.

Load balanced - Multiple servers with equal priority. Sending servers choose randomly, distributing load.

Hosted email - Google Workspace, Microsoft 365, and other providers use their MX records (e.g., aspmx.l.google.com).

MX Lookup Applications

Deliverability troubleshooting - When email bounces, verify MX records exist and point to functioning servers.

Migration planning - Before switching email providers, document current MX configuration. Plan cutover by updating MX to new servers.

Provider identification - MX records reveal what email service a domain uses. Useful for sales intelligence and competitive analysis.

Security assessment - Outdated or misconfigured MX records indicate potential email infrastructure problems.

Reverse MX Lookup

Find all domains using a specific mail server. Enter a mail server hostname to discover:

  • Every domain routing mail through that server
  • Customer lists for email providers (Google Workspace, Microsoft 365, etc.)
  • Shared mail infrastructure relationships

Use cases: competitive intelligence, email deliverability analysis, identifying phishing infrastructure.

→ Check MX records on robtex.com

FAQ

What if a domain has no MX records?
Mail servers fall back to the A record - they'll attempt delivery directly to whatever IP the domain resolves to. This is uncommon and often indicates misconfiguration.
What priority should my MX records use?
Convention uses values like 10, 20, 30 for primary, secondary, tertiary. The actual numbers don't matter - only their relative order.
Why do MX records point to hostnames, not IPs?
DNS design requires it. MX records must contain hostnames, which then resolve to IPs via A records. This allows mail servers to change IPs without updating every sender's cache.
How do I verify my MX setup works?
Send test emails from external addresses and verify delivery. Check MX records resolve to valid, responding mail servers.
How do I find all domains using a mail provider?
Use reverse MX lookup. Enter the mail server hostname (e.g., aspmx.l.google.com) to see all domains with MX records pointing to it. A "Previously MX for" section shows domains that used to use this mail server.
Can I see which domains previously used a mail server?
Yes. The "Previously MX for" section appears below the current "MX for" table. It lists domains that historically routed email through this server but have since switched providers — useful for tracking email migrations.