i'm wondering: after we received a boss-scam mail that was showing the faked From in the webinterface, i read a bit about how SPF is checked, and apparently it is checked against the Return-path and not the From header. (This reddit was good summary https://www.reddit.com/r/sysadmin/comments/20rnt6/smtp_question_does_spf_only_validate_the/ )
Whats the benefit of this? As far as i can see, this renders the whole idea almost useless, as it doesnt prevent spammers from sending spam with faked From headers at all. What am i missing here?
(This is just because i'm wondering, i'am aware that DKIM + DMARC will solve this spam problem :) )
Don't try to make SPF responsible for something it's not. SPF simply lists which servers can send mail for your domain. It checks the envelope sender (MAIL FROM) at the SMTP level, which is the value that ends up in the return-path header, but only after it's passed SPF checks. What you're saying is that (assuming you have a strict SPF policy) you're allowing someone to send fake mail from one of your own mail servers, which is a problem much further up the chain than the From header, and one that would not be solved by DKIM. Perhaps your SPF record is not strict enough? We can't tell from the information you posted.