The spamtrap feature is a "spamtrap and hamtrap aliases on a per-domain level".
When checking the mail.log I see mails to spamtrap@domain.tld delivered to /var/virtualmin-traps/spam/
That does look more like a domain independent feature. Which is good because all my clients can use the same spamtrap@myvirtualminserver.tld address for sending spam.
So what exactly does "per-domain level" mean?