The dovecot antispam plugin watches a defined spam folder (defaults to "SPAM"). It works together with a spam system that classifies each message as it is delivered. When the message is classified as spam, it shall be delivered to the spam folder, otherwise via the regular filtering file the user may have (maildrop, sieve, ...). Now the user has everything classified as spam in the special spam folder, everything else where it should be sorted to.
This is a companion discussion topic for the original entry at https://copr.fedorainfracloud.org/coprs/pipiche/dovecot-antispam-plugin/