Cannot send emails in outlook express?

Yahoo Plus Mail in Outlook Express-Won't send emails. HELP!!!?

• I have used Yahoo Plus! for 3 years and never had any trouble sending or receiving into Outlook Express. Recently I changed ISP from Time Warner to AT&T and now I cannot get Outlook to send any of my outgoing messages. I have checked the POP3 settings for incoming and outgoing and have checked my user name and password and have the box to require authentication checked to use the same settings as my incoming mail. I don't know what else to do. Does anyone have any GOOD advice for me? below is the error message I receive when I try to send emails. "Outlook cannot connect to your outgoing (SMTP) e-mail server. If you continue to receive this message, contact your server administrator or Internet Service Provider (ISP)."

• Answer:

  Troubleshooting tips If you still can’t send Yahoo! Mail from your mail program, you may be accessing the Internet through an ISP that is blocking the SMTP port. If this is the case, try setting the SMTP port number to 587 when sending email via Yahoo!'s SMTP server.