Mail processing with custom script on Postfix and Plesk (plesk_virtual)

I'd like to parse incoming mail with custom script. Something which would be easily done with [man aliases(5)](http://www.postfix.org/aliases.5.html) for real users or with [procmail](https://unix.stackexchange.com/questions/145771/mail-filtering-with-procmail-in-a-postfix-dovecot-system-with-virtual-users/148095#148095) [for vitual users](https://unix.stackexchange.com/questions/79046/extracting-attachments-from-mail-that-is-coming-to-my-postfix-inbox) . But on my system is is plesk and setup is: virtual_transport = plesk_virtual, thus I cannot put configure it as virtual_transport = procmail. What is plesk_virtual anyway, where are the configuration files, documentation? ("plesk_virtual" site:https://docs.plesk.com/ finds nothing, [Mail doc](https://docs.plesk.com/en-US/obsidian/advanced-administration-guide-linux/services-management/mail-service.68762/) neither).