Error on receiving email

I made a fresh install of Virtualmin in a new server and I cannot receive emails. The sender gets this message

5.1.1 Recipient address rejected: User unknown in virtual alias table.

I assume this is because my server is an AWS EC2 instance and there could be some issue with the private and public IP. The reason I am saying that is because I have tried to install Virtualmin in Ubuntu 18.04, Debian 9.5 and CentOS 7 (using this one now). They all have the same problem.

I searched the forum before posting that. I saw some people had issues with DNS. I think I am good with that. I am not an expert on this field but I checked my DNS using online testers. It seems to be good, unless there is something I am missing.