SPFs

SPFs, the plural of SPF, commonly refers to two domains: sun protection and email authentication. In dermatology, SPF stands for Sun Protection Factor, a measure of how well a sunscreen protects against ultraviolet B (UVB) radiation, which causes sunburn. The SPF value is defined as the ratio of the minimal erythemal dose with sunscreen to the dose without sunscreen. Higher numbers indicate greater theoretical protection, but protection is not perfectly proportional to SPF. Most products also advertise broad-spectrum coverage for UVA rays, and some specify water resistance for defined periods. Effective protection depends on applying a sufficient amount and reapplying every two hours or after swimming or sweating, as well as using shade and protective clothing.

In information security, SPF stands for Sender Policy Framework. An SPF record is a DNS entry that lists mail servers trusted to send messages on behalf of a domain. When a recipient receives a message, the mail system can check the domain’s SPF record to verify whether the sending host is authorized. SPF helps reduce email spoofing and phishing, especially when used with DMARC and DKIM. Limitations include that SPF does not verify the visible From header, can fail with forwarded mail, and can be misconfigured, potentially causing legitimate mail to be rejected or spam to pass. Proper deployment involves publishing a correct SPF record with the appropriate mechanisms (for example ip4, ip6, include) and monitoring DNS lookup limits.

SPFs as a term therefore appear in both health and technology contexts, with unrelated meanings.