Note that DMARC modifies the meaning of SPF. SPF without DMARC protects the envelope-sender and not the From header. With DMARC SPF protects the From header as

Note that DMARC modifies the meaning of SPF. SPF without DMARC protects the envelope-sender and not the From header. With DMARC SPF protects the From header as well. SPF, DKIM, and DMARC maybe useful against fishing. In the long run it doesn't do anything against spam. So it is rather unfortunate that gmail (certainly on IPv6) is so eager to classify mail without those headers as spam.