Follow the steps to enable the Postfix SSL for SMTP in the Virtualmin server:
1. Login to Virtualmin control panel. https://xx.xx.xx.xx:1000.
2. Click Edit Virtual Server. Go into Enabled Features and check the “ Setup SSL website too? ”, then hit save.
If the web server is nginx then the option will be ” Nginx SSL website “
3. Edit /etc/postfix/master.cf. Find these lines and uncomment them:
# smtps inet n - n - - smtpd
# -o smtpd_tls_wrappermode=yes
# -o smtpd_sasl_auth_enable=yes
# -o smtpd_client_restrictions=permit_sasl_authenticated,reject
# -o milter_macro_daemon_name=ORIGINATING
4. Restart SSL AUTH daemon
# /etc/init.d/saslauthd restart
5. Server Configuration -> Manage SSL Certificate and Click the button “Copy to Postfix” at the bottom. That’ll setup Postfix with that new SSL cert you just created.
6. Restart mail server
# /etc/init.d/postfix restart