SPF and DKIM are not enough to harden email. Email can still be spoofed through a loophole in both specs.
See https://www.nslookup.io/learning/dmarc-a-practical-guide/
See https://www.nslookup.io/learning/dmarc-a-practical-guide/
and this quote is not correct:
> Note that an email doesn't need to pass both DKIM and SPF. Just one is enough to validate an email.
Unless it was said in regards to DMARC, it usually depends on the mailfilter of the receiver. If it was said in regards to DMARC then it's just another point why DMARC is bad.