You need to contact your email service provider ie gmail , roadrunner , atnt or check in the webmail

As far as I am aware my email service provider is Mozilla Thunderbird.

Thunderbird is email client software not a provider.

email providers are like gmail , hotmail , yahoo mail or it can be your internet service provider as well like comcast , at&t , coz etc or it can be your domain provider what email address do you use??

cornelis@ntlworld.com - sorry for the bother but I am far from expert on this matter. Your help is much appreciated.

Try here.

I shall direct my enquiry to Virgin Media. Many thanks for your help, it is much appreciated.

Sure , thats the best way to resolve this issue