Messages are not being sent

When I try to send messages, the messages get stuck in the outbox and this is the error that shows up:

The host '*** Email address is removed for privacy ***' could not be found. Please verify that you have entered the server name correctly.

Subject 'Re: Recipes'
Server: '*** Email address is removed for privacy ***'
Windows Live Mail Error ID: 0x800CCC0D
Protocol: SMTP
Port: 25
Secure(SSL): No
Socket Error: 11003

However, when I log on to Eastlink Webmail, the messages, including the messages with attachments, go through with no problem using the exact same outgoing server that Windows Live Mail says cannot be found. After reading other posts, not being able to find outgoing servers from a number of  different service providers seems to be an ongoing issue with Windows Live Mail. I'd PREFER to use Windows Live Mail, but I now have Eastlink Webmail on my desktop as a backup, so it's not a critical situation for me. Anyone have any idea why this issue persists with Windows Live Mail?