Using Thunderbird client, we are suddenly receiving Relay access denied 554 5.7.1 errors attempting to send to any domain but our own. This function was working and has suddenly stopped. We have tried all of the different options within Outbound Server configuration (No, TLS, if available, TLS Only, SSL) to no avail. We do have proper username and password information. We have enabled "Enable Authentication". We can receive email with no problem, but outbound mail will not work. We are able to send and receive from the local network. This only fails when outside of the LAN. We do have TLS authentication checked. Although, we have tried it with and without TLS.