SPF and sender id have nothing to do with spam...
they allow one to check if the email is allowed from comming from that server

this will make very hard for someone to fake a email from other people, and so spam and virus will get rejected...

BUT there is nothing that forbides the spammer from buying a domain, setup the SPF and send the spam, and so, SPF isnt about spam, but building the link about who send the email and who the emails claim to be

of course in the end, if one can trust the from:, we can whitelist the good domains and blacklist the bad ones
the bad ones will always keep changing, but the true gain will be the trust in the whitelist and the end of abusing other people domain

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