Postfix Issue: Connection Timed Out

From the Roundcube dashboard, it shows that the message is sent successfully. However, when I check into /var/log/mail.log, it shows like this: https://pasteid.fledix.com/5mat It's not even receiving messages from other emails. * I went to _Hostname_ and _DNS Client_ in _Network Configuration_ and changed the DNS servers to 127.0.0.1, 8.8.8.8, and 8.8.4.4. (It had only one: that is my dedicated IP) * I restarted saslauthd and postfix several times. * I changed the TLS to default for the Dovecot server. * I am a total layman. One thing that struck me is that when I log into the Webmin panel, the system hostname shows as my chosen hostname (xxx.xxx.xxx.xx), where xxx.xxx.xxx.xxx is my dedicated IP. In other Webmin installations, I have seen it shows as the hostname (127.0.1.1). Can anyone please help me out?