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The SPF mechanisms

An SPF record defines the authorized mail servers for a domain. It specifies the IP addresses or hostnames of authorized mail servers allowed to send emails on behalf of that domain.

The following mechanisms are used in an SPF record:

  1. a: Matches the IP address of the domain's A record.
  2. mx: Matches the IP address of the domain's MX record.
  3. include: Includes the SPF record of another domain.
  4. ptr: Matches a reverse DNS lookup of the IP address.
  5. ip4: Matches a specific IPv4 address.
  6. ip6: Matches a specific IPv6 address.
  7. exists: Matches an address listed in a specified domain.