- SPF records are single TXT records starting with v=spf1; any syntax error invalidates the entire record.
- Eight mechanisms exist: all, include, a, mx, ptr, ip4, ip6, exists; each either matches the client IP or not.
- Qualifiers (+,-,~,?) set the result when a mechanism matches; default is + (Pass).
- Modifiers like redirect= and exp= provide extra information; redirect= hands evaluation to another domain after all mechanisms fail.