The mail server "smtp.mail.yahoo.com" is for Yahoo Mail Plus users. If you have subscribed to this Yahoo mail service then you must provide authentication information along with the mail server name - "smtp.mail.yahoo.com". In WebCam Monitor, you can provide the user name and password by checking the "My Outgoing mail server requires authentication" option under "Configure Mail Server". If you do not specify a mail server then WebCam Monitor automatically tries to determine the mail server's address from the e-mail's domain name. If you are using any e-mail client like Outlook or Outlook Express, you can copy the SMTP settings to "Outgoing Mail Server" dialog in WebCam Monitor.