How SPF Works SPF Flattening records for domain names (DNS) that specify rules for their domains are published by domain owners. An SPF record is plain text, and it could be as straightforward as a single line listing the IP addresses allowed to e-mail on behalf of the domain. When an email server received an incoming email, it conducts DNS searches to find the SPF domain record and examines the domain displayed in the return path of the message. read full review »