Ubuntu Postfix: Mail loops back to myself and host greeted me with my own hostname

Solution 1:

You have not configured Postfix to accept mail destined for the neonnuke.tech domain, but you have configured the MX record to point to this mail server. Postfix has no idea what to do with this mail upon finding that it has received the very mail it is trying to send.

To resolve the problem, you need to tell Postfix to accept mail for neonnuke.tech, for instance by adding it to mydestination or virtual_alias_domains.

For bonus points, you are getting the message about the host greeting me with your own hostname, because the server is behind a NAT of some kind, and thus does not know it is reachable on its global IP address. This also will go away once the mail server knows it is authoritative for mail for the domain.