olemus
SPF-süsteemis: aktsepteerimine, kuid kahtlasena
= in the SPF system: acceptance, but with suspicion

ülevaateid
https://postmarkapp.com/blog/explaining-spf

https://blog.zensoftware.co.uk/2014/09/02/what-are-spf-sender-policy-framework-records-all-about/