spam sending in fresh cyberpanel installation

On a fresh installation of cyberpanel, and just after 24 hours, the DC informs me that the VPS is used for sending spam (note that I have not yet configured an account on this VPS, only the hostname of the server in order to have a valid SSL certificate)
Can you please help me protect myself against sending spam by advising me on the different settings to be made (Postfix / Dovecot or others).

For the moment, here is what I have done but I am afraid that it is not enough:
In /etc/postfix/, I added the following line:
smtpd_sasl_security_options = noanonymous

In /etc/postmaster/, I replaced the hostname ( with the hostname of the VPS

I also installed and configured SpamAssassin on the VPS and I deactivate the mail function in php.ini (on all the existing PHP versions on the VPS)
I also activated the function of limiting the number of sending emails.

Any help is welcome