Here are the basic server settings for Yahoo! Mail:
Incoming Mail (POP3) Server:	plus.pop.mail.yahoo.com (Use SSL, port: 995)
Outgoing Mail (SMTP) Server:	plus.smtp.mail.yahoo.com (Use SSL, port: 465, use authentication)
Account Name/Login Name:	Your Yahoo! Mail ID (your email address without the "@yahoo.com")
Email Address:	Your Yahoo! Mail address (e.g., user@yahoo.com)
Password:	Your Yahoo! Mail password


In case you have the mail plus account. Here's the code. 

        Dim oMailMessage As New MailMessage("frommail@yahoo.com", 
"tomail@yahoo.com", "Test Mail", "Hello World This is just a test")
        Dim oSmtpClient As New SmtpClient
        oSmtpClient.Host = "plus.smtp.mail.yahoo.com"
        oSmtpClient.EnableSsl = True
        oSmtpClient.Port = "465"
        oSmtpClient.Credentials = New System.Net.NetworkCredential("murugan_ad", "******")
        Try
            oSmtpClient.Send(oMailMessage)
        Catch ex As Exception
            TextBox1.Text = ex.ToString
        End Try



send me a mail to  in case you 
have trouble