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SPF Flattening — the practice of replacing SPF mechanisms that trigger DNS lookups with resolved IP address mechanisms to reduce lookup count, at the cost of keeping addresses synchronized.
SPF checks whether the sending IP is authorized to use the domain in SMTP MAIL FROM or HELO. It does not authenticate the visible From address or protect message content; DMARC also requires domain alignment.
SPF Flattening — the practice of replacing SPF mechanisms that trigger DNS lookups with resolved IP address mechanisms to reduce lookup count, at the cost of keeping addresses synchronized.
The receiver retrieves the domain’s SPF record, evaluates its mechanisms for the sending IP in order, and produces pass, fail, softfail, neutral, temperror, or permerror.
Publish one SPF record, authorize only real senders, stay within the ten DNS-mechanism lookup limit, and choose the correct all qualifier. Test both syntax and the actual sending IP after changes.
