Postfix how to rewrite headers correctly?

Question

postfix

Hello! There is a mail system based on freebsd+postfix+cyrus imap. Sometimes letters like [email protected] come from external servers, which cirus doesn't like very much and as a result the letter is discarded. It turns out that there is a need to edit the headers. As I understand it, this is achieved by writing a line in main.cf, for example, header_checks=regexp:/usr/local/etc/postfix/header_checks
And in the file itself, this line
/^To: (.*)@MYDOMAIN\.RU/ REPLACE To: [email protected]
But for some reason this scheme doesn't work. Still the To: field does not change. Please advise what needs to be done to resolve this issue.