email message in vb.net but I got this error

hi,
I use this code for email message in vb.net but I got this error
The transport failed to connect to the server. How to solve

Dim EmailTo As String     'Emailaddres for user to send
        Dim EmailFrom As String   'Emailaddres for user from 
        Dim MailSubject As String 'Subject of Mail
        Dim MessageBody As String 'Message
        Dim ServerName As String  'Server Name - important


        ServerName = "spiro47"
        'Similarly, add in EmailTo, EmailFrom etc parameters here
        EmailTo = "sekar.mca2009@gmail.com"
        EmailFrom = "raja.mca2010@yahoo.com"
        MailSubject = "welcome"
        MessageBody = "hi"

        'Set the SMTP Server's address
        SmtpMail.SmtpServer = ServerName
        Try
            SmtpMail.Send(EmailFrom, EmailTo, MailSubject, MessageBody)
        Catch ex As Exception
            MsgBox("Delivery Failure: " & ex.Source & ex.Message)
        End Try

regads
sekar.c

Regards
Sekar.c