I had to sign up with a major SMTP provider last year and they wouldn't accept my regular email for login, which is on a very regular normal domain. They asked me to sign up with a major email like gmail. I was luckily in a position to refuse, and complained until they updated their rules.
I wonder if your government also has a declaratively nationalist discourse.
I mean, it's great to be independent, just make your infrastructure rely on the services of an US based company...
This really shouldn't be allowed in this day and age but I'm effectively powerless to change it. DeGoogling is hard.