current version of the SPF spec具体说明：

SPF records MUST be published as a DNS TXT (type 16) Resource
Record (RR) [RFC1035] only. The character content of the record is
encoded as [US-ASCII]. Use of alternative DNS RR types was
supported in SPF’s experimental phase but has been discontinued.

In 2003,when SPF was first being developed,the requirements for
assignment of a new DNS RR type were considerably more stringent than
they are now. Additionally,support for easy deployment of new DNS
RR types was not widely deployed in DNS servers and provisioning
systems. As a result,developers of SPF found it easier and more
practical to use the TXT RR type for SPF records.

In its review of [RFC4408],the SPFbis working group concluded that
its dual RR type transition model was fundamentally flawed since it
contained no common RR type that implementers were required to serve
and required to check. Many alternatives were considered to resolve
this issue,but ultimately the working group concluded that
significant migration to the SPF RR type in the foreseeable future
was very unlikely and that the best solution for resolving this
interoperability issue was to drop support for the SPF RR type from
SPF version 1. See Appendix A of [RFC6686] for further information.

The circumstances surrounding SPF’s initial deployment a decade ago
are unique. If a future update to SPF were developed that did not
reuse existing SPF records,it could use the SPF RR type. SPF’s use
of the TXT RR type for structured data should in no way be taken as
precedent for future protocol designers. Further discussion of
design considerations when using new DNS RR types can be found in
[RFC5507].

作为旁注,在您的示例中还有一个发件人ID记录(不幸的是,它被称为“spf2.0”,尽管它是一个不同的规范),该类记录的规则仍然是实验性的,match the experimental version of the SPF spec,没有更新发布.