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It's is a change in mail service behavior, and arguably either a broken policy or broken spec (not sure and don't really care since the effect is the same). "I

• Avamander 3y ago
  It's really not a change or any of those. Mail services have behaved this way in some form or way for a while, these specs have worked like this from the start and the policy is only a logical conclusion of it all. Untrusted forwarders (also sometimes known as open relays) have been heavily frowned upon for a really long time. SPF has never worked for forwarders that don't do rewriting. Those letters have always been negatively looked upon, unauthenticated mail is a remnant of times long gone. Google's policies about authentication are the bare minimum you should be doing anyways if you care even a little bit about your customers or recipients in general.