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Just to make it clear, is this true if you use your own domain, or just if you use any of Fastmail's domains?

• Riverheart 8y ago
  Seems to be just Fastmail domains but there might be some setup involved for custom domains. See their docs https://www.fastmail.com/help/technical/senderauthentication.html https://www.fastmail.com/help/technical/senderauthentication...
  • eggsampler 8y ago
    I have received a spoofed email from my own domain, so I believe it's not just Fastmail domains but any custom domain on an account.
    • Riverheart 8y ago
      Do you host your custom domain with Fastmail? I may have misread but the article seemed to suggest you could potentially setup dmarc via the DNS page or whoever you host with.
  • bscphil 8y ago
    If I understand this correctly, you need to be managing your own DNS (not letting Fastmail do it), and you probably need to set p=reject in your DMARC so that non-fastmail servers can't spoof your addresses. And if Fastmail allows Fastmail user A to spoof Fastmail user B, then the above still only protects you against non-Fastmail customers.