SPF (Sender Policy Framework) is an email authentication method used to prevent email spoofing and phishing by verifying that the sender of an email is authorized to send messages on behalf of a particular domain. SPF records are DNS records that specify the authorized mail servers that are allowed to send email on behalf of a domain.

When an email server receives an incoming email, it can check the SPF record of the sender’s domain to verify whether the sending server is included in the list of authorized mail servers for that domain. If the sending server is not listed in the SPF record, the receiving server may treat the email as suspicious or reject it, depending on the configured SPF policy.

An SPF record consists of a simple syntax that defines the permitted mail servers and their corresponding IP addresses or IP address ranges. Here’s an example of an SPF record:

v=spf1 ip4:192.168.1.10 include:mail.example.com ~all

In this example:

  • “v=spf1” indicates that this is an SPF record.
  • “ip4:192.168.1.10” authorizes the IP address 192.168.1.10 to send email on behalf of the domain.
  • “include:mail.example.com” allows any mail server listed in the SPF record of “mail.example.com” to send email for the domain.
  • “~all” indicates that any other mail servers not listed in the SPF record are considered “neutral.” The “~” character means a “soft fail,” which means the email may still be accepted but marked as suspicious.

SPF records can include various mechanisms to define authorized servers, such as IP addresses, IP address ranges, and domain names. Organizations can customize SPF records based on their email infrastructure and sender policies.

When setting up an SPF record, it’s important to carefully consider the mail servers that are authorized to send email on behalf of the domain. Misconfigurations or outdated SPF records can lead to email delivery issues. Additionally, SPF records work best when combined with other email authentication methods like DKIM and DMARC to provide a comprehensive email security strategy.