Is it possible to block sending mail for specific sites?

Question

PHP

Hello. There are:
debian + postfix + nginx-fpm + php7.4 (if anything, the version is unimportant) + virtualmin
Need to:
Prohibit sending any mail from certain sites (pieces ~ 175). For simplicity - at first to one.
In the internet I found:
php_admin_value[sendmail_path] = /dev/null
in the php config to register for the domain. Any other ideas? (I don’t like it because virtualmin can restart the config. Like: for some reason I clicked “save nginx-fpm settings” - and it will take it and overwrite it.)