Sending emails

I can no longer send emails. I can send them through mail web browser and was in touch with their technical support and the problem is not on their end. The message I get when trying to send an email is: "Sending of message failed. The message could not be sent because connecting to outgoing server(SMTP) Promail.ptd.net failed. The server may be unavailable or is refusing STMP connections. Please verify that your outgoing server (STMP) settings are correct and try again". I checked my outgoing server settings and they are correct. I started Thunderbird in Troubleshoot mode and the problem still occurs. I started my Windows 10 in Safe Mode and the problem still occurs.