Email text not rendering with correct charset (cyrillic)

Email text not rendering with correct charset (cyrillic)

There is a problem with rendering cyrillic characters in both the e-mail subject and e-mail body. In the case of the subject I get multiple question marks and the body of the e-mail gets characters like this:  тест. I have tested it with 3 other emails i.e. Gmail, Outlook, etc. but do not get the same problem. Can you please look into it and suggest a course of action that will solve the issue. 

Thank you!