When you manage your domains through Fastmail it does it automatically. I certainly haven't had to configure it myself.
There is a neat website to check your email settings that was on the HN front page earlier this year:
There is a neat website to check your email settings that was on the HN front page earlier this year:
Please read my blog here: https://www.uriports.com/blog/introduction-to-spf-dkim-and-d...
It will explain how SPF, DKIM, and DMARC work together to prevent spam.
This is the original submission where the link came from if it helps: