Ask HN: FreeTaxUSA denies registrations based on TLDs in email addresses?

I’ve been trying to register on their website with my non-mainstream email address ending with a geographical TLD and I got this error:

The email can't be a foreign email address ending with <TLD in my domain name>

Out of curiosity I tried with some other domain I have around ending with different geographical TLDs and the error is always the same.

Support mentioned that it’s due to “regulations” but I find this very hard to believe.