Problem sending from the server

Hello, how are you
I have a problem sending from the server
  I have a complete server and the board has been installed, installed and the settings have been adjusted
But the mail in the server receives emails but does not send them at all.
I hope to help

First thing to check is to contact the upstream to make sure the SMTP port is open.
With some providers (like Vultr), all you have to do is request it via support ticket.

After that, install s-nail (dnf install s-nail), and try a test from the CLI:

echo "Example Message" | s-nail - s "A mail sent using s-nail" person@example.com

If you get the test, the SMTP port is open and everything should work.