If you’ve been running ActiveSync on a dedicated subdomain with Horde you’ve probably been relying on Apache Alias directives to get it working.
Now mod_php is deprecated, you don’t have that option.
You now have to set the handler for the /usr/share/psa-horde folder in Additional directives for HTTPS for the subdomain in Plesk.
I copied this over from the main webmail conf, the only change I made was to change PHP version to 7.4.
Horde PHP Handler
FcgidInitialEnv PP_CUSTOM_PHP_CGI_INDEX plesk-php74-fastcgi
FcgidInitialEnv PP_CUSTOM_PHP_INI "/etc/psa-webmail/horde/horde/php.ini"
<Files ~ (\.php$)>
FCGIWrapper /var/www/cgi-bin/cgi_wrapper/cgi_wrapper .php
Require all granted
I hope that helps someone.