In this example, this error appears when attempting to connect to a Postfix email server from a Windows machine in the LAN using a command line prompt. Following are things to check:
- Ensure you can ping and tracert from the Windows machine to the email server
- Ensure port 25 is open on the email server. This can be done using Nmap. If port 25 is not open:
- Open port 25 in iptables on the email server
- Use the /sbin/service postfix status command to ensure the Postfix email service is running
- Ensure the /etc/postfix/main.cf file has inet_interfaces set to "all"