It's annoying that my real mailbox isn't allowed here

[Red Herring]

I tried to register with my real e-mail and it was declined, so I had to use a trash mail to register. It seems yandex is bad because it has .ru domen while some instant randomly generated email without registration is perfectly fine because it has .com domen. I personally find it offensive.

[Grey]

Sorry, but the amount of spam from .ru and .cn domains is unbelievable. We have various other domains blocked too.

[Marson]

Many of these issues come down to pure statistics and have nothing to do with personal views.

[Faeryan]

This doesn't fix the issue but you could use some email forwarding address, a so-called alias.