ip6 mechanism
The SPF mechanism that matches an IPv6 address or network written directly in the record, such as ip6:2001:db8::/32, without any DNS lookup.
What it means
ip6 is the IPv6 counterpart of ip4. ip6:2001:db8::25 names one address; ip6:2001:db8::/48 names a network. With no prefix length it means a single address (/128). Like ip4, it requires no DNS query and does not count toward SPF's limit of ten lookups.
It matters whenever a server can reach receivers over IPv6. An IPv4-only record gives an IPv6 connection no match, so the result falls through to the record's default (often softfail or fail). Gmail is strict about IPv6: it expects mail arriving over IPv6 to come from an address with a PTR record and to pass authentication, and rejects mail that does not.
Check whether your mail servers or providers send over IPv6 before assuming the IPv4 list is complete.
Example
v=spf1 ip4:203.0.113.10 ip6:2001:db8:1::/48 -allRelated terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 7208: Sender Policy Framework (SPF), section 5.6rfc-editor.org
- Google: Email sender guidelinessupport.google.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes