Hi all what spam filter are you using and your experience?
We use SpamHero.com for inbound and outbound filtering/delivery. Almost no false positives and seems to do a really good job blocking the junk. We’ve also had a few instances where a mailbox was compromised and they do a really good job of identifying that quickly and stopping just outgoing mail from that account while allowing the rest to send normally. They probably aren’t right for every scenario. But we run our own SmarterMail server as well as some cPanel servers. We just alias all domains going to each server through a single account to keep costs reasonable. But in some cases we separate out domains to give our clients more control over their filtering.
Stock 365 filters with a few custom rules here. No third-party filter, never found it necessary since moving to 365. You can tweak the policy as needed. Seems to work pretty well.