This was brought on by attempting to send an email with attachments to a large contact list (270).  Deleting all emails in the Outbox and restarting the computer have not solved the problem.  Now I can't send emails at all, regardless of number of recipients.  I am receiving them, however.

Complete error message:

The connection to the server has failed.

Subject 'Re: Address'
Server: 'smtp-server.roadrunner.com'
Windows Live Mail Error ID: 0x800CCC0E
Protocol: SMTP
Port: 43
Secure(SSL): No
Socket Error: 10060

When I reset the outgoing port to 587, a new message pops up:

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 '*** Email address is removed for privacy ***', please contact your email service provider.

Subject 'Re: Address'
Server Error: 451
Server Response: 451 Outbound mail refused - 69.203.12.145 - See http://www.timewarnercable.com/en/residential-home/support/topics/internet/email-setup.html [R0209002]
Server: 'smtp-server.roadrunner.com'
Windows Live Mail Error ID: 0x800CCC79
Protocol: SMTP
Port: 587
Secure(SSL): No

Hope you can help!