What is the recommended way to process buggy SPF (DNS TXT) records?

Question

Given an SPF record with one or more invalid entries.

Eg: v=spf1 ip4:1.2.3.4/24 ip6:fe80:0::/64 fe80:1::/64 mx ~all

As you can see there is an invalid entry (missing ip6: mechanism) following 2 valid ones. What is the recommendation, what should the SPF validator report? Should it pass (provided that the sender matches the first or second rule) or should it hardfail due to parse error?

I guess most MTA do softfail, because I came across an SPF record like this on a fairly popular service, and people complains only on delayed delivery, not on not delivering at all.

Answer 1

This is discussed in section 8 of rfc 7208 - https://www.rfc-editor.org/rfc/rfc7208#section-8

If I understand it correctly as per 8.7 a "Permerror" should be returned. Handling this is then left up you the system. This is stated in multiple places, most notably G 6.3 which (of hard errors) says " As with all results, implementers have a choice to make regarding what to do with a message that yields this result"

I put to you that as the zone has a (tilde) at the end the expectation is that if in doubt the email should be allowed as per the publishers request. You may be able to allow it and subject it to more critical spam analysis?