How to solve constant encoding reset when sending or forwarding messages in Outlook 2016?

Question

Character encoding

Good afternoon. One user has such a problem: when replying to an incoming letter or forwarding it, the encoding is constantly reset instead of UTF-8, either KOI8-U or WINDOWS is selected. Setting the default encoding of outgoing messages to UTF-8 in the mail client settings does nothing. All the same, it resets and as a result, the recipients see krakozyabry instead of intelligible text (on any clients). You have to change it manually every time, which is not very convenient. Reinstalling office didn't help either. Communigate Pro mail server. The problem is only with one user, everyone else is fine.