Configure

$ doas pkg_add rspamd opensmtpd-filter-rspamd

The default configuration is fine for most use cases, so we'll just leave it there.

However you can add the following line to your smtpd.conf

filter rspamd proc-exec "filter-rspamd"

Also add rspamd after dkimsign in the authcheck part, mentioned in [[Opensmtpd.Configure]]

authcheck = "pki example.com auth <passwd> filter { check_rdns check_fcrdns dkimsign rspamd }"

After done, restart smtpd with

$ doas rcctl restart smtpd