[Hardwired8976]

Question for people with fastmail and a .net custom domain: Do you usually get blocked sometimes? I wanted to send an email to my therapist and one email to my insurance but both had blocked me. A mailbox.org address worked just fine. Is it because of the domain or because of the .net ending?

[Avamander]

I'd propose a third and a fourth reason - your domain's volume is too small and its security setup isn't top-notch.