Mail headers will indicate scanners are working:
scanners: regex: 1.4.0 attach: 1.4.0 clamav: 0.103.2/m:62/d:26347 spam: 3.4.6 rspam: 2.7 dspam:  3.10.2 (agent/library)

To troubleshoot simscan, clamav, spamc, rspamd, or dspam add 'SIMSCAN_DEBUG="5"' to tcp.smtp, reload cbd (qmailctl cdb) and
watch output of smtp log. You should see something like the following:
2020-10-15 13:14:54.487439500 simscan: runned_scanners is  attach: 1.4.0 clamav: 0.102.4/m:59/d:25957
2020-10-15 13:14:54.487447500 simscan: found 0.102.4/m:59/d:25957
2020-10-15 13:14:54.487447500 simscan: normal clamdscan return code: 0
2020-10-15 23:20:18.803403500 simscan: calling spamc
2020-10-15 23:20:18.803412500 simscan: calling /usr/bin/spamc  spamc
2020-10-15 23:20:20.417465500 simscan: cdb looking up version spam
2020-10-15 23:20:20.417467500 simscan: runned_scanners is  regex: 1.4.0 attach: 1.4.0 clamav: 0.103.2/m:62/d:26347 spam: 3.4.6 rspam: 2.7 dspam:  3.10.2 (agent/library)
2020-10-15 23:20:20.417468500 simscan: found 3.4.2
2020-10-15 23:20:20.417468500 simscan:[4629]:CLEAN (0.30/12.00):1.9820s