I'm on Debian stable, not OpenBSD, but SpamAssassin + razor + pyzor works really well. Roughly 1 spam per month, and 1-2 false positives a year. This is for an email address that has been used and openly spread widely for 25+ years.
The real work is making sure that outbound mail gets delivered, but even that is just making sure you have a clean IP and setting up reverse DNS + DMARC/SPF/DKIM...