Check the DNS resolution of the client sending mail, because it seems is not resolving mail.satimis.com.
Oct 16 09:16:15 xen01 postfix/smtp: 51DD82055B: to=<firstname.lastname@example.org>, relay=none, delay=1.1, delays=1.1/0.01/0.05/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=mail.satimis.com type=A: Host not found)
From here I see your zone is ok, but I can't telnet to port 25 of mail.satimis.com, so I think you should open the port in your router/fw if you want receive mail from the internet.
Bmw M2B15 History