[Virtual Basic] l'e-mail

Bonjour

J'ai voulu faire un logiciel pour ma famille, mes amis et moi pour envoyer des e-mail ( depuis le logiciel ).
Cependant aprés mon codage, une erreur apparaît : L'exeption SmtpException n'a pas été géree.

Voici mon codage :

Public Class Form1

    Private Sub Label4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label4.Click

    End Sub

    Private Sub Label5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Label5.Click

    End Sub

    Private Sub GroupBox1_Enter(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles GroupBox1.Enter

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        GroupBox1.Enabled = False
        GroupBox2.Enabled = True
        Button2.Enabled = True
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        Dim mail As New MailMessage
        Dim SMTP As New SmtpClient("smtp.gmail.com")

        mail.From = New MailAddress(TextBox1.Text)
        mail.To.Add(TextBox3.Text)
        mail.Subject = TextBox4.Text
        mail.Body = TextBox5.Text

        SMTP.Port = "25"
        SMTP.Credentials = New System.Net.NetworkCredential(TextBox1.Text, TextBox2.Text)
        SMTP.EnableSsl = True

        SMTP.Send(mail)

    End Sub
End Class

L'erreur se fait a la dérniére ligne a SMTP.Send(mail)

Cordialement