ATTENTION:

Please make sure that you read /var/qmail/doc/PORT_NOTES.
It contains important information about testing and configuring
qmail, and finally replacing sendmail with qmail.

You should also add /var/qmail/man to your MANPATH (see manpath(1)
or login.conf(5)).

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

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

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

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

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