MX Records in Brief
A domain’s MX (Mail Exchanger) records tell other servers where to deliver email for that domain. For example, a company using Google Workspace has MX records pointing to Google’s mail servers. You can see any domain’s MX records with our DNS Record Lookup, or learn the command-line way in How to look up MX records with nslookup and dig.
What a Reverse MX Lookup Does
A reverse MX lookup answers the opposite question: which domains use this mail server? You enter a mail server hostname such as mx1.example-host.net and get a list of domains whose MX records point to it.
DNS itself cannot answer this question. There is no record that lists “all domains using this server”. A reverse MX tool therefore relies on a database built by collecting MX records of many domains over time. Our Reverse MX Lookup uses the MX records observed in lookups made on this site, so its coverage grows with use.
Practical Uses
Mail Migrations
Hosting companies and IT teams use reverse MX data to find every domain still pointing to an old mail server before it is shut down.
Troubleshooting Shared Mail Servers
If mail delivery fails for one domain, checking which other domains share the same mail server helps decide whether the problem is the server or the domain’s own configuration.
Security and Investigations
Phishing and spam campaigns sometimes register many domains that share the same self-hosted mail server. Reverse MX data can reveal those related domains. The same idea applies to nameservers with our Reverse NS Lookup and to web servers with Reverse IP Lookup.
Market Research
Looking at which domains use a small, specialized mail provider can show who its customers are.
Why Results Are Never Complete
- Coverage: no database contains every domain on the internet. Results show domains that were observed, not all domains.
- Freshness: MX records change. A domain listed today may have moved since it was observed.
- Huge providers: for mail services such as Gmail or Microsoft 365, millions of domains share the same mail servers. A list of them says little about any single domain, so reverse MX is most informative for small or self-hosted mail servers.
How to Read the Mail Server Name
MX hostnames often reveal the provider: names ending in google.com or googlemail.com indicate Google Workspace, names ending in mail.protection.outlook.com indicate Microsoft 365, and names that contain the hosting company’s domain usually point to shared hosting mail. A name inside the domain itself, such as mail.example.com, typically means a self-managed or hosting-panel mail server.