This is a new domain on an IP that was fairly recently assigned to it. All main email providers blacklist anything that is not gmail, outlook or aws by default. Nothing I can do about it, other than becoming part of the problem and paying them to host this instance’s email.
Host my own email as well and received it just fine.
Yes, same here. SpamAssassin checks content, while the big providers simply run a whitelist that only really has other providers as the first gatekeeper.