Reverse MX shows all domains with the same mail server | WhoisXML API

Reverse MX products to identify connected domains via different consumption models

We offer different ways—Lookup, API, Database—to check which domains are connected by a mail server.

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500 free API requests. No credit card required.

50 Billion+Domains and subdomains
BillionsMX records
52,000+Satisfied customers
14+Years of data crawling

Our reverse MX product line includes:


Simply type in a mail server address on our functional graphical user interface (GUI) to get a list of all the domain names that share it.

Reverse MX Lookup | WhoisXML API
Reverse MX API | WhoisXML API


Reverse MX API allows you to see other domains that share the same mail server via API calls. It can be used in conjunction with existing security systems.

DNS Database Download

Our reverse mail server services glean data from DNS Database Download, one of the most extensive passive Domain Name System (DNS) repositories in the world. As a result of more than 12 years of data crawling, our database has amassed millions of mail server and nameserver records and billions of historical DNS records.

DNS Database Download | WhoisXML API


  • Constantly updated and comprehensive

    The passive DNS database that provides data for our reverse MX services is updated every week, further adding millions of historical DNS records. The database contains more than half a million MX records for billions of domains and subdomains.

  • Responsive and integrable

    Reverse MX API can be easily integrated into existing systems as it supports various programming languages that include JavaScript (JS), Java, C#, NodeJS, Perl, PHP, PowerShell, Python, and Ruby on Rails (ROR). The passive DNS database can also be downloaded in full as a MySQL dump or comma-separated values (CSV) file.

Product Usage

  • Blacklisting Prevention

    Avoid mail server blacklisting and the consequent damage that can do to your email deliverability and domain reputation. Use our reverse MX solutions to pinpoint bad hosts that may be connected to spamming or malicious activities.

  • IoC List Expansion

    Expand your list of indicators of compromise (IoCs) and potentially related artifacts. Use our reverse MX tools to uncover connected domains that may otherwise seem unrelated to threats.

  • Third-Party Risk Assessment

    Assess how vulnerable specific third parties are to threats and compromise. Use our reverse MX solutions to analyze an organization's mailing functions by gaining insights into its network structure and possible security vulnerabilities.

  • Threat Hunting

    Collect as much data as possible on threats and possibly their perpetrators. Use our reverse MX tools to do extensive research on potentially malicious mail servers and connected web properties.

Reverse MX Overview | WhoisXML API

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