SPF has nothing to do with the From header. And the DKIM signature does not have to match the sender’s domain, the signature can be that of any domain. This means that for practical purposes, anybody can send spoofed emails. That an email is signed with DKIM, that doesn’t mean much and it is meant to build a web of trust between servers, but otherwise it is useless for the users themselves.
They wrote a blog post about how SPF/DKIM work: https://fastmail.blog/2016/12/24/spf-dkim-dmarc/
If you want to let people know which emails are from you, the From address is very weak. This is because the From/To headers tell you nothing about the source and the destination of the message, according to the email standard. Read that blog post for details.
You need a proper signature via PGP or S/MIME if you want to ensure that the receiver knows the message is from you. And unfortunately this requires education and email clients with support for such signatures (most desktop clients do), but that’s email for you.
