Mail Exchange (MX) records are DNS records that specify the mail servers responsible for receiving email messages on behalf of a domain. These records play a crucial role in directing email traffic to the appropriate mail servers. MX records are essential for proper email delivery and are used by email systems to determine where to send incoming email messages.

Key points about MX records:

  1. Email Routing: MX records define the mail servers that will handle incoming email messages for a domain. Each MX record includes a priority value (a number) and the hostname of the mail server.
  2. Priority: MX records have a priority value that indicates the order in which mail servers should be used for email delivery. The lower the priority number, the higher the priority. Email is typically routed to the mail server with the lowest priority value.
  3. Hostname: The hostname in the MX record specifies the fully qualified domain name (FQDN) of the mail server responsible for receiving email messages. This hostname must have corresponding A (IPv4 address) or AAAA (IPv6 address) records that point to the actual IP addresses of the mail servers.
  4. Multiple MX Records: A domain can have multiple MX records with different priority values. This provides redundancy and failover capabilities. If the highest-priority mail server is unavailable, email will be delivered to the next highest-priority mail server.
  5. DNS Lookups: When sending email, the recipient’s mail server performs DNS lookups to find the MX records for the sender’s domain. It then uses the MX records’ priority values to determine the order in which to attempt email delivery.
  6. TTL (Time-to-Live): Like other DNS records, MX records have a TTL value that determines how long the DNS resolver caches the information.
  7. Preference Number: The term “preference number” is often used interchangeably with “priority” in the context of MX records.
  8. Subdomains: MX records are typically configured for the root domain (e.g., example.com), but they can also be configured for subdomains (e.g., mail.example.com).
  9. Mail Exchange Servers: MX records point to mail exchange servers, which are responsible for receiving, storing, and delivering email messages to the recipient’s mailbox.
  10. Email Routing Rules: MX records are a fundamental part of the email routing process. They help ensure that email messages are sent to the correct destination based on the recipient’s domain.

MX records are a crucial component of the email infrastructure and are used by email systems worldwide to ensure the reliable delivery of email messages to their intended recipients.