How to encrypt Postfix easily?
Just add the following rules at the end of the config file /etc/postfix/main.cf:

# SSL/TLS parameters
smtpd_tls_cert_file=/path/to/your/certificate
smtpd_tls_CAfile=/path/to/your/bundle
smtpd_tls_key_file=/path/to/your/keyfile
smtpd_use_tls=yes
smtpd_tls_auth_only = yes
smtp_tls_security_level = may
smtpd_tls_security_level = may
# For TLS Logging uncomment the following
#smtp_tls_loglevel = 1

Now restart postfix and monitor your maillog.

# service postfix restart

or

# /etc/init.d/postfix restart