In that case need to check the firewall opening port for the zimbra server.

Another solution is you can check with your ISP provider that which port for SMTP that them uses. The default port for SMTP is Port 25. Some ISP now using 587 as their SMTP port. After confirm that thing, Please check your mail server configuration in your router whether you use the same port as you...

ask2me007
You can check your public IP of mail server MX Lookup Tool - Check your DNS MX Records online - MxToolbox or sorbs.net

You try this
https://192.168.1.104:7071/zimbraAdmin