Setup Postfix to send with smtp.mailfrom as a wordpress@wordpress-site.tld

Currently, Postfix on my Virtualmin host sends mails with smtp.mailfrom: (as set in /etc/hostname).

Is there a way for it to pick up the domain current PHP app is running?

I have multiple VirtualMin accounts running Wordpress apps, and I’d like to emulate the wp_mail behaviour under cpanel accounts these sites were migrated from.