What do you use for email hosting when you have 30+ domains?

255 days late but anyway

Okay but what's the actual false positive rate on that. No way you're checking 600 rules for overlap or ordering bugs. I had maybe 40 on a RackNerd setup once and still found mails vanishing into the void because two rules contradicted.

Also OP if you're still around, did you ever solve this. The "clients who barely know what DNS is" part is the real killer, anything without a panel they'll call you for every password reset.

255 days late but did you ever solve this? I was in basically the same spot last year, 30-ish domains on a KnownHost box that started crawling during the morning mail queue. Ended up moving the heavy users to a HostHatch storage VPS and kept the light ones where they were. Deliverability actually got better because the IPs were warmed already. Clients never noticed except the ones who suddenly stopped getting blacklisted to spam.

Still curious if you tried the Hostinger route Carl mentioned, their site is a mess to navigate.