Can't use my personal email domain

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1

I’m trying to use my personal email for registering, but I get an error from Discorse:

Email is not allowed from that email provider. Please use another email address.

Email is not allowed from that email provider. Please use another email address.
Email is not allowed from that email provider. Please use another email address.1098×285 12.6 KB

I’m trying to use a personal domain `****@conto.dev` that I have hooked into Fastmail. Does anyone know what might be blocking registration? I’ve never seen this before on other sites, including other Discorse forums.

2

I ran into the same issue while registering my account today. Why would Universal Blue choose to disable the use of email domains which every other organisation I have relations with accepts without a fuzz?

I even have DNSSEC, DANE, DKIM, SPF et al in place. I also provide E-Mail-Services to customers, even to government agencies, yet U.B. apparently considers my domains unworthy?