Does anyone know how #fastmail gets the avatars for email senders?

I know it's not BIMI as neither news.philips-hue.com nor philips-hue.com have BIMI records.

I know it's not Gravatar as neither of the two email addresses returns anything from Gravatar.

So, how does Fastmail do it? I'd love to know if anyone knows.

#email #fastmail