Incoming messages are not affected, but outgoing messages go nowhere. I've pasted the complete error message below. Any ideas? (I wonder whether a recent update to Norton Security Suite changed something.)

The connection to the server has failed.

Subject 'test'
Server: 'smtp.comcast.net'
Windows Live Mail Error ID: 0x800CCC0E
Protocol: SMTP
Port: 25
Secure(SSL): No
Socket Error: 10060