Sender Policy Framework (SPF) is an email authentication method designed to detect forged sender addresses in emails (email spoofing), a technique often used in phishing and email spam.
SPF allows the receiver to check that an email claiming to come from a specific domain comes from an IP address authorized by that domain's administrators. The list of authorized sending hosts and IP addresses for a domain is published in the DNS records for that domain.
Sender Policy Framework is defined in RFC 7208 dated April 2014 as a "proposed standard".

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    SPF failing

    I have recently enabled SPF, DKIM and DMARC on my NAS running mailserver. All seemed to be working fine until I got messages from people trying to send me mail that it was bouncing. On investigation, it only when the MailServer perfoms an spfquery on an incoming message and the response is too...
  2. WST16

    SPF, DKIM and DMARC. 2019-04-11

    If you’re a brave soul who’s feeling adventurous and about to embark on setting up your own mail server on your DiskStation, this is a very helpful article that explains SPF, DKIM and DMARC.