What email filtering technique verifies that an email is from a trusted IP address?

The technique that verifies an email is from a trusted IP address is SPF, which stands for Sender Policy Framework. SPF allows domain owners to specify which IP addresses are permitted to send emails on behalf of their domain. When an email is received, the recipient's mail server checks the SPF record of the sending domain against the IP address from which the email was sent.

If the sending IP address is included in the SPF record, the email is more likely to be legitimate, helping to prevent spoofing and unauthorized use of the domain. This is particularly important for protecting against phishing attacks and ensuring the integrity of email communication.

In contrast, other techniques like DKIM (DomainKeys Identified Mail) deal with verifying the integrity of the message itself and its authenticity through cryptographic signatures, while DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds upon SPF and DKIM to provide comprehensive reporting and policy enforcement. Blacklisting involves blocking known malicious IP addresses but does not specifically validate whether an email originates from a trusted IP associated with a given domain.