Windows 10, Live Mail Version 2012 (Build 16.4.3528.0331) ISP Virgin Media using email name .... @ntlworld.com.

As from yesterday 01-01-18 I cannot send from my main account.  My sub-email accounts send OK.  The Live Mail settings in each of the accounts including the main account are all the same.  I have not changed anything in the main account settings.  I can send from my main account on the ISP webmail.

I desperately need to send emails from Live Mail.  Please can anyone advise on how to resolve this issue?

Thank you in advance.  Sally