email can't be sent out(message does not meet IPv6 )

Our system has detected
that this 550-5.7.1 message does not meet IPv6 sending guidelines regarding
PTR records 550-5.7.1 and authentication.

This is what I got when I tried to send email to my gmail from my VPS. From webmin’s “read user mail” I can see the test mail I sent from my gmail, but when I tried to reply I got the above message. What could be the problem?

My website is up and running. On domain management I only set a mxe record pointing to my vps’s IP. Then on virtualmin I just created a new user for email as instructed on virtualmin’s documentation page. Now I can get email but outgoing is not working.

mate whats your server settings about dkim and dmarc? is your ip blocked somewhere? did you check all of those?

I am using virtualmin and everything is by default. It is a new server, I don’t think the ip is blocked anywhere