ATTENTION:

Do not forget to read %%PREFIX%%/doc/TLS.readme. After all,
this is NOT our old stock qmail.

You can enable qmail as your default mailer executing:
> %%PREFIX%%/scripts/enable-qmail

==> As you need to provide a working certificate in %%PREFIX%%/control/cert.pem :

# makes a self-signed certificate
3) do "make certificate"

# makes a certificate request
4) do "make certificate-req"