What is a mail exchanger?

A mail exchanger (MX) is a type of record within the Domain Name System (DNS) record that specifies the mail servers responsible for receiving emails on behalf of a domain: MX records act as the postal addresses of email servers, ensuring efficient routing for emails associated with a particular domain.

The DNS is akin to the internet's address book, translating human-readable domain names (e.g., gmail.com) into IP addresses that computers use to locate each other on the network (for instance, or 2a00:1450:4002:414::2005): when someone sends an email to an address associated with a specific domain (e.g., batman@gmail.com), the email server uses DNS to look up the MX records for the recipient's domain, then it establishes a connection with the identified mail server using the SMTP protocol and initiates the email transfer.

To inspect MX records for a domain, you can use DNS query tools such as dig in Linux and MacOS or nslookup in Windows. For instance, in Linux and MacOS, you can query the MX records of the domain gmail.com using the following command:

dig +short gmail.com mx

And in Windows you can query the same using the following command:

nslookup -q=mx gmail.com

In both cases, the result will resemble the following:

5 gmail-smtp-in.l.google.com.
30 alt3.gmail-smtp-in.l.google.com.
40 alt4.gmail-smtp-in.l.google.com.
10 alt1.gmail-smtp-in.l.google.com.
20 alt2.gmail-smtp-in.l.google.com.

Email verification is a meticulous process, and within our advanced email checker, the analysis of MX records and the subsequent connection to mail exchangers constitutes a crucial phase: by scrutinizing MX records, our system validates the authenticity of the designated mail servers associated with a domain, ensuring that they are configured correctly and ready to receive emails. Learn more about how we verify email addresses.

Anatomy of MX Records

Each MX record includes two main components - the mail server and the priority.

The mail server is the fully qualified domain name (FQDN) or IP address of the mail server assigned to receive emails for the domain. In the example above, the mail servers are gmail-smtp-in.l.google.com, alt3.gmail-smtp-in.l.google.com, etc.

The priority is a numerical value that indicates the preference of the mail server. Lower values denote higher priority. In scenarios with multiple MX records, email servers prioritize the server with the lowest value: when multiple MX records are present, email servers attempt to deliver emails to the server with the lowest priority first and, if that server is unavailable, the next lowest priority server is tried. In the example above, the priorities are 5, 30, etc.

In the case of gmail.com, email servers will first attempt to deliver emails to gmail-smtp-in.l.google.com because it has the lower priority of 5; if that server is unavailable, only then will emails be directed to alt1.gmail-smtp-in.l.google.com and so on.

MX records play a crucial role in the email delivery process, ensuring that emails are routed correctly to the designated mail servers for a given domain: understanding and configuring them correctly is essential for maintaining a reliable and efficient email infrastructure.

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