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...