Okay, you have a number of problems, most/all of which should be fixable!
- You need a public hostname for the server, which rDNS pointing back to it. server.example.com is good if you don’t have a specific domain.
1.1 Once you’ve done that, you’ll need to update the server to use that hostname for mail. Iff the top of my head, adding it to/etc/mailname(and replacing anything already there) should do the job for mail purposes. -
Enable DKIM - you’ll probably need to copy the key from
/srv/example.com/config/dns/example.com.txtand add that to the DNS with the same ‘selector’ - Add a DMARC record. Theres a good online generator at mxtoolbox.com.
If you sort those out, it should significantly improve the score.