MX Lookup

How to read MX records

An MX record pairs a priority with a mail server hostname. Here’s a domain with a primary and a backup server:

example.com.  3600  IN  MX  10  mx1.mailhost.example.
example.com.  3600  IN  MX  10  mx2.mailhost.example.
example.com.  3600  IN  MX  20  backup.mailhost.example.

Senders share the load across the two priority-10 servers and only use the priority-20 backup if neither answers. The 3600 is the TTL: resolvers may cache this answer for an hour. Hosted providers often need just one record: Google Workspace now uses a single 1 smtp.google.com.

Common MX problems

No MX records

Senders fall back to the domain’s A record, which is usually a web server that doesn’t accept mail, so messages bounce. Add the records your email provider gives you.

A mail server that doesn’t resolve

The hostname has no A or AAAA record, often because of a typo or an old provider that was shut down. Senders skip it, and if it’s the only one, mail bounces.

MX pointing at a CNAME or an IP address

Both break the standard. Point the MX record at the hostname your provider gives you, not at an alias or a raw IP.

Leftover records from an old provider

After switching providers, old MX records can split your mail between two systems. If the tool shows two different providers, remove the one you no longer use.

Null MX (0 .)

Not a mistake: the domain is saying it never receives email (RFC 7505). It’s common on parked domains and domains used only for a website. Don’t publish it on a domain you send from, because bounces and replies have nowhere to go.

Related tools

• Free email verifier Check whether a specific address exists.
• Catch-all checker See if a domain accepts mail for any address.
• SPF record checker Check which servers may send mail for the domain.
• DNS record checker Look up every record type at once.