mkesmtpdcert — Create a secure SMTP test certificate
/usr/sbin/mkesmtpdcert
Secure ESMTP requires a valid, signed, X.509 certificate. The default
location for the certificate file is /etc/courier/esmtpd.pem.
The mkesmtpdcert generates a self-signed X.509 certificate,
mainly for testing. For production use the X.509 certificate must be signed by
a recognized certificate authority, in order for mail clients to accept the
certificate.