Outlook Express Email wont send error message 0x800CCC0F

My Yahoo webmail still works fine but last Friday my Outlook Express stopped sending emails and produced the following error message;

 

Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'mail.btinternet.com', Server: 'mail.btinternet.com', Protocol: SMTP, Port: 25, Secure(SSL): No, Error Number: 0x800CCC0F

 

I use Norton 2011

 

After spending 2 days on the telephone to BT support in India the problem remains unresolved. What has been identified is that Outlook Express will not hold a password when set, it loses it immediately I return to send an email. The Outlook Express account has been deleted and reset but the problem still exists. The indian support said that the error number related to a firewall issue but I thought it was a server problem even though my webmail is working fine.

 

I installed Firefox Thunderbird and had problems with that in as much that when I input my password it said that the server had rejected it.

 

So, has Norton done something to my Outlook Express? My problems started around 21/22 July 2011, was there a Norton update around that time and if so, did it include an email update?

 

I need to use Outlook Express as my webmail through BT Yahoo is attrocious. Can anybody help please as I have busted my guts over this.

 

Thanks

 

PS I have tried all of the normal things