Troubleshooting Postfix email issues can be a multistep process. If you are receiving a connection refused error when attempting to send email from Postfix, try these troubleshooting steps:

1. Restart the Postfix service

Sometimes there is a pending configuration change that wasn't properly applied. Restart the Postfix service and then any emails in the queue should clear out automatically. Run the command: systemctl restart postfix

2. Check the system firewall

Sometimes, the system firewall may prevent outgoing email. You can temporarily disable the firewall to see if this resolves the issue.

3. Use telnet to check if the receiving side has port 25 open

Make sure that telnet is installed (you can use the command which telnet) and then issue the command telnet mail.server.com 25 and then see if you get a connection. If you do get a connection, then the other side is not rejecting the connection and it could be another issue. To close the connection, type Ctrl + ] and then you will be returned to a telnet> prompt. From here, type exit to return to your server console.

If none of these work, please open a support ticket and our team can help you diagnose the issue.