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