from field encoding

Good day. I have a dovecot 2.3.4.1 on debian 10 as an imap server. I found there are emails where the header field From has no encoding even if there is a name with special characters like Žlutý Kůň. The header looks like:

From: "Žlutý Kůň" <zluty.kun@domain.tld>

In this case the email client - roundcube, outlook etc. will show the From with wrong characters. This behaviour is typical only for dovecot, not for courier-imap - it was installed before dovecot with no problems.

If there is corretly encoded From filed, the client shows the From correctly.

Is there a way to set up the dovecot to show the field correctly even without encoding stuff? Some default/fallback settings?

Thank you very much for your help

Jan Jurko