The message could not be sent. The setting for your outgoing email [SMTP] server might need to be configured. To find the server settings for '<Unknown>', please contact your email service provider.

Subject 'Proof of Identity'
Server Error: 501
Server Response: 501 #5.1.1 bad address
Server: 'smtp.talktalk.net'
Windows Live Mail Error ID: 0x800CCC79
Protocol: SMTP
Port: 25
Secure(SSL): No

I cannot send email for all three addresses. The port numbers are the same as on my other system as are all the checked boxes.
Very  frustrating, any advice please.
Thank you.