The Bat! Mail System (shareware) have good Russian language support including KOI8-R support.
You don't need KOI8-R fonts with The Bat! since the program uses standard Windows CP1251 fonts with a decoding table.
Before installing The Bat! International Pack (do it if you want to have Russian menus and diagnostics) run The Bat! and check following settings in the Account|Properties tab:
- In the Transport section check that 8-bit characters are treated is set to Without changes.
- In the Options section check that Allow 8-bit characters in message header is set to off (unchecked).
- In the Templates|New message section set Use Character set to
When you got any message in your folders, choose it to bring it to the lower view panel, then in the View|Encoding menu choose Cyrillic (KOI-8), then again go to the View|Encoding menu and choose Set as default