Da haben wir ja mal wieder etwas dazu gelernt, Herrschaften:

Die IETF hat im April 2014 mit RFC 7208 einen Proposed Standard veröffentlicht, nach dem SPF-Einträge ausschließlich als TXT Record erfolgen dürfen.

In Abschnitt 3 des RFC heißt es“. “SPF records MUST be published as a DNS TXT (type 16) Resource Record (RR) only. 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.”

Das komplette Dokument finden Sie unter: RFC 7208 – Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1