Filter name: Delete at once
Filter enabled: Yes
Scope: Matching any of the following rules
Rules: From Contains xxxxxxx@yyyyyyy.com
Action: Delete message
Mail from xxxxxxx@yyyyyyy.com is always spam and lands in the spam folder. After implementing the filter above in Roundcube I expected those emails to disappear, but they still go to the spam folder.
I found this old forum topic: Roundcube filter to keep spam in inbox, and although it doesn’t offer a resolution, maybe it will give you some ideas about what’s going on.
It’s very possible that this is some odd interaction going on between spamassassin and the sieve filter.