Enable rejection / discarding of emails at mailserver level based on the sender, sender domain or host

[ccfu]

In reference to this post, it would be good if emails from specific senders and hosts could be rejected or discarded before they reach users' mailboxes. Currently, unless the IPs are on a blocklist the only way to achieve this is by blocking the IP via the network settings (but this is only effective if the spam comes from the same IP or range). Mails from specific senders or hosts that are not classified as spam can be discarded with filters, but as soon as they are classified as spam the filter is ignored. This doesn't seem logical.