Connection to server fails using outlook express trying to send

In Outlook Express my incoming mail server is pop3 and is set to "pop.yahoo.com" My SMTP server is "smtp.comcast.net" I use Yahoo web for my email reception but send from Outlook Express. Suddenly, I cannot send an email. The error message is "The connection to the server has failed. Account: 'pop.yahoo.com', Server: 'SMTP.COMCAST.NET', Protocol: SMTP, Port: 25, Secure(SSL): No, Socket Error: 10060, Error Number: 0x800CCC0E.
This is a brand new problem. Any help?