Good point, they know mail.ru is used by spammers. So they probably limit to Russia IPs.
I had the same problem on IG. If used mail.ru, can not create accounts! However using yahoo/hotmail works! But than I switched back to mail.ru as yahoo requires phone verification after some time and you would need all those phone numbers... I does not work same as IG, weher you can put custom IP.
On the other side Hotmail sucks (MS product), try to change password... You have to go through many steps....
Gmail seems the best one.