Check that these are set to true, and if not, set them to true and restart amavisd and the MTA

$ zmlocalconfig antispam_enable_rule_updates

antispam_enable_rule_updates = false

$ zmlocalconfig antispam_enable_restarts

antispam_enable_restarts = false

$ zmlocalconfig -e antispam_enable_rule_updates=true

$ zmlocalconfig -e antispam_enable_restarts=true

$ zmamavisdctl restart

$ zmmtactl restart