SPF: No 'grandchild trick' in e-mail correspondence

The Sender Policy Framework (SPF) was created to combat unauthorized tampering with IP addresses on mail servers. Essentially, the administrator of a domain stores the IP addresses of all authorized senders ('Mail Transfer Agents' - MTA) for the mail recipient to view. The receiving system retrieves this SPF information for the specified domain via the Domain Name System (DNS). It compares the IP address of the sending MTA with the permitted addresses. If the IP address matches the verified MTAs, the sender is considered authentic. Otherwise, the email is discarded or at least a warning is issued. Participation in the SPF system and making SPF records visible is voluntary.

Although SPF can also be used to prevent garbage and phishing, the Sender Policy Framework is not a spam prevention program. It merely serves to detect forged sender addresses 'on the envelope' of an email.