I have followed the guide below to create a firewall rule to block spam using spamhaus. Are there additional services or sites like spamhaus that I can use in a similar way. I want to maximize spam blocking as much as I can.
https://docs.opnsense.org/manual/how-tos/edrop.html (https://docs.opnsense.org/manual/how-tos/edrop.html)
Thank You
Adguard or Pi-Hole are common spam blockers
There is no pihole for opnsense.
If you use unbound as your dns you can set up blocklists directly: https://docs.opnsense.org/manual/unbound.html#blocklists
Or if you want to use adguard home, it's available from mimugmail 's community repo.
There is also a whole thread about it https://forum.opnsense.org/index.php?topic=22162.0
Spam is a whole lot better dealt with on the mailserver itself, or a spam filtering box in front of the real mailserver. Perhaps look at os-rspamd.
DNSBL can be part of some spam scoring, should rarely be used for outright rejection of mail exept for very small amount of well-known offenders. On that note, many of the Spamhaus blocklists are well known for collateral listing and problematic policies / politics.