Problems sending emails with Windows Live Mail on Windows 7

Hello,
I have just started using Windows Live Mail a few weeks ago. I sent a mass email out to a bunch of people regarding a club event. A message pops up saying:

The message could not be sent. The setting for your outgoing email server might need to be configured. To find the server settings for 'email address', please contact your email service provider.

Windows Live Mail Error ID: 0x800CCC79

Now every time I exit Windows Live it says you have unsent messages in your inbox, do you want to send them now? When I push yes, the same message as above comes up. And when I exit the program and restart it, I cannot send emails but I can recieve them.

Any help on how to get rid of this message and fix the problem would be greatly appreciated.

Thanks in advance.