Summary
You have activated TLS via Administration > IMSS Configuration > SMTP Routing > Connections > Transport Layer Security Settings. This works fine for the incoming mails but your outgoing mails are still being sent without TLS.
You cannot find any other option in the web console to enable TLS for outgoing mail.
Details
IMSS can use TLS when it acts as SMTP server. To enable this, modify the Postfix configuration file:
- Open the Postfix configuration file, main.cf.
- Add the following parameter and set its value to "may":
/etc/postfix/main.cf:
smtp_tls_security_level = may - Save and close the main.cf file.
- Restart the postfix using the command below:
#service postfix restart
After configuring this setting, IMSS will now act as SMTP client and the server will support TLS. Thus, IMSS can use TLS to transmit the message.
For additional information, refer to this Postfix article: SMTP Client specific settings.
