MX Lookup

What This Tool Does

This tool resolves the MX records on any domain, then for each MX it also looks up the A records and reverse DNS (PTR). It checks for common misconfigurations that break mail delivery, and pattern-matches the MX hostnames against 25+ known mail providers to identify what platform the domain uses for email.

The Checks We Run

• MX presence. Are there any MX records published? Without them the domain cannot receive mail.
• Priority ordering. MXes returned in priority order (lowest = preferred). Multiple priorities = redundancy.
• Hostname resolution. Each MX hostname must resolve to A/AAAA records. We flag any that don't.
• CNAME violation. RFC 2181 forbids MX records pointing to CNAMEs - most mail servers reject. We detect and flag.
• Reverse DNS (PTR). Each resolved IP should have a PTR. Missing PTR downgrades sender reputation.
• Single point of failure. Only one MX = no redundancy. We recommend a backup.
• Provider detection. Pattern-match against 25+ known mail providers (Google Workspace, Microsoft 365, Zoho, etc.).

What MX Records Actually Are

An MX (Mail Exchanger) record is a DNS entry telling the world where to deliver mail for your domain. Each MX has two parts: a priority number (lower = preferred) and a hostname. When someone sends mail to [email protected], the sending server queries DNS for example.com's MX records, sorts them by priority, and attempts delivery to the lowest-priority MX first.

Example MX configuration:

example.com.  IN  MX  10  mx1.example.com.   ; primary
example.com.  IN  MX  20  mx2.example.com.   ; backup if mx1 down
example.com.  IN  MX  30  mx3.example.com.   ; third tier

If mx1 is unreachable, sending servers try mx2 after a brief retry. If mx2 also fails, mx3. Mail typically queues at the sender side for 4-5 days before bouncing back.

Common MX Mistakes

• MX pointing to CNAME. RFC 2181 explicitly forbids this. Use A records as the MX target.
• No backup MX. Single MX = single point of failure. Even a low-priority Cloudflare Email Routing or external backup is better than nothing.
• Missing PTR on sending IPs. Mailbox providers downgrade reputation for senders without forward-confirmed reverse DNS.
• Trailing dot mistakes. MX target hostnames need a trailing dot (FQDN) - without it, your DNS provider may append the zone again creating broken records like mx1.example.com.example.com.
• Pointing MX to the bare domain. Some setups use example.com as the MX target - works but discouraged. Use a dedicated subdomain.

Frequently Asked Questions