What email header field helps prevent sender address forgery?

The email header field that helps prevent sender address forgery is SPF, which stands for Sender Policy Framework. SPF is an email authentication protocol designed to allow the recipient's mail server to verify that incoming mail from a domain comes from a host authorized by that domain's administrators. This is achieved by the sender creating an SPF record in their DNS settings that lists the IP addresses or hosts that are permitted to send email on behalf of their domain.

When an email is sent, the receiving mail server checks the SPF record against the IP address of the mail server that sent the email. If it matches, the email is considered valid; if not, it may be flagged as suspicious or rejected. By utilizing SPF, domain owners significantly reduce the risk of address spoofing and fraudulent activities since only authorized servers can send emails on behalf of the domain.

Other methods, such as DKIM (DomainKeys Identified Mail) and DMARC (Domain-based Message Authentication, Reporting, and Conformance), also contribute to email security and preventing forgery but in different ways. DKIM focuses on attaching a digital signature to emails that recipients can use to verify authenticity, while DMARC builds on SPF and DKIM to provide more stringent policies for how email receivers should handle messages that fail