Systems-Edge help page.  Error sending emails from BT home broadband
Outlook Express reports: Some error occurred while processing the required tasks.
Please review the list of errors below for more details.

The error message says
An unknown error has occurred. Account: 'your name',Server: 'smtp.your host.com'Protocol
SMTP.Server Response: '421 your email hosting server.com connection refused
from (your ip address),Port 25, Secure(SSL): No Server Error. 421, Error Number: 0x800ccc67.

If you can read emails ok from outlook express but cannot send
the problem is caused by  BT blocking port 25 for un-validated email accounts.
Many users phoning BT pay 50P per minute trying to resolve the issue
and after expensive phone calls they fail to resolve the problem.
Users resort to using webmail.

The solution is very simple.
Change the port from 25 to 465

Outlook Express
TOOLS   ACCOUNTS   MAIL

Click on your account to change
Type in 465 in outgoing mail SMTP
Tick this server requires a secure connection SSL
Save the settings with APPLY