need email function help!

using asp.net to send an email to my account(gmail), however it has been unsuccessful.
Web.config file 
<system.net>
<mailSettings>
<smtp>
<network
host="smtp.gmail.com"
/>

</smtp>
</mailSettings>
</system.net>
 
Email.aspx
Protected Sub btnSend_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSend.Click

SendMail()

End Sub

Private Sub SendMail()

Dim mailMessage As New System.Net.Mail.MailMessage

  mailMessage.From = New MailAddress("testing@gmail.com")
  mailMessage.To.Add(New MailAddress("testing@gmail.com"))

mailMessage.Subject = txtSubject.Text.Trim()
mailMessage.Body = txtBo ...