I've been having same problem since last week when TalkTalk upgraded to "next generation network". Have gone through checks with them but they are saying the problem is not with them. When sending email from ALL 3 of my toucansurf.com accounts using Windows Live Mail this message comes up:

Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity.

Subject 'TEST1'
Server: 'smtp.toucansurf.com'
Windows Live Mail Error ID: 0x800CCC0F
Protocol: SMTP
Port: 25
Secure(SSL): No

but not when I send from my talktalk.net email address !!

Split from an unrelated thread