Domains need to be warmed, too
One thing that came out of the ISP session at M3AAWG is that domains need to be warmed up, too. I can’t remember exactly which ISP rep said it, but there was general nodding across the panel when this was said.
This isn’t just the domain in the reverse DNS of the sending IP, but also domains used in the Return Path (Envelope From) and visible from.
From the ISP’s perspective, this makes tons of sense. Some of the most prolific snowshoe spammers use new domains and new IPs for every send. They’re not trying to establish a reputation, rather they’re trying to avoid one. ISPs respond by distrusting any mail from a new IP with a new domain.