The SPF redirect trap: why -all can make redirect= useless

The SPF redirect trap: why -all can make redirect= useless SPF records often look simple until you start combining mechanisms and modifiers. One particularly easy mistake is to write a record like this: v=spf1 include:_spf.google.com -all redirect=_spf.example.com At first glance, it seems reasonable: authorize Google, reject everything else, and use another SPF policy through redirect= . But the redirect= part will never be used. The reason is an important detail of how SPF evaluation works. redirect= is not a fallback after -all An SPF record is evaluated mechanism by mechanism. For example: v=spf1 ip4:192.0.2.10 include:_spf.google.com -all The receiver checks the mechanisms until one matches. The all mechanism is special because it always matches . That means: -all effectively says: If nothing before this matched, return SPF Fail. Now consider this record again: v=spf1 include:_spf.google.com -all redirect=_spf.example.com Once SPF reaches -all , it already has a result. There is no reason to evaluate redirect= . The redirect modifier is only used when none of the mechanisms in the record produce a match. Because all always matches, a record containing all prevents redirect= from being used. What redirect= is actually for The redirect modifier is useful when several domains should share one central SPF policy. Imagine these domains: example.com example.net example.org Instead of maintaining the same SPF configuration independently on every domain, they can redirect to a central policy. For example: example.com TXT "v=spf1 redirect=_spf.example.com" example.net TXT "v=spf1 redirect=_spf.example.com" example.org TXT "v=spf1 redirect=_spf.example.com" And the central record might contain: _spf.example.com TXT "v=spf1 ip4:192.0.2.10 include:_spf.google.com -all" Now the sending policy can be maintained in one place. This is very different from include: . redirect= vs include: These two are easy to confuse. include: Use include: when you want to authorize senders def