I wonder if the lack of an SPF DNS record is a factor in the decision to mark a message as spam.
I understand that an SPF fail is definitively such a factor, i.e. when SPF is configured, but a message has "MAIL FROM" / "Return-Path" domain not on the list in the SPF record.
But is the consequence of not setting SPF only letting spammers roam free? Or does it also "de-value" legitimate emails from my domain in spam algorithms, because there's no way to check?
In other words, assuming spammers don't currently spoof emails from my domain much, may adding SPF improve deliverability of legitimate messages?