I have a 5 year old HP windows 7 still using WIndows Live, i have bt internet mail and can receive but cannot send. I have spoken to Btinternet. and to Microsoft and they cannot help suggested i ask on here as they do not support anymore

I have a small business and I cant send anything out. Ca someone help me please , its urgent

An unknown error has occurred.

Server: 'mail.btinternet.com'
Windows Live Mail Error ID: 0x8007007A
Protocol: SMTP
Port: 25
Secure(SSL): No

and 

Server: 'mail.btinternet.com'
Windows Live Mail Error ID: 0x8CCC0002
Protocol: SMTP
Port: 25
Secure(SSL): No

Please help