I manage IT at a mid-size business. At least once a month, I get asked to release some incoming email from quarantine that got sent there because the sender's SPF record is wrong or outdated and doesn't include all the email services they actually use. (What this really tells me is how many small businesses are out there running with no in-house IT expertise or support of any kind.)
I don't do whitelisting. Instead, I always reach out and offer to help the other party correct their SPF record.
It happens often enough that I wrote a script in Racket that will generate the email for me and paste it into the clipboard [1]. The email tells them exactly what they need to change, and links to docs from their current email provider (so they don't have to trust me about edits to their DNS).
[1]: https://gist.github.com/otherjoel/6b8bf02f6db6e0c47ba6bca72e...
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