Private Sub EmailTextBox_Validating(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles EmailTextBox.Validating
    Dim temp As String
    temp = EmailTextBox.Text
    Dim conditon As Boolean
    emailaddresscheck(temp)
    If emailaddresscheck(conditon) = False Then
        MessageBox.Show("Please enter your email address correctly", "Incorrect Email Entry")
        EmailTextBox.Text = ""
        EmailTextBox.BackColor = Color.Blue
    Else
        EmailTextBox.BackColor = Color.Green
    End If

End Sub


Private Function emailaddresscheck(ByVal emailaddress As String) As Boolean
    Dim pattern As String = "^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$"
    Dim emailAddressMatch As Match = Regex.Match(emailaddress, pattern)
    If emailAddressMatch.Success Then
        emailaddresscheck = True
    Else
        emailaddresscheck = False
    End If
End Function

Private Sub EmailTextBox_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles EmailTextBox.TextChanged
    EmailTextBox.BackColor = Color.White
    Dim temp As String
    temp = EmailTextBox.Text
    Dim conditon As Boolean
    emailaddresscheck(temp)
    : If emailaddresscheck(conditon) = True Then
        MessageBox.Show("Please enter your email address correctly", "Incorrect Email Entry")
        EmailTextBox.Text = ""
        EmailTextBox.BackColor = Color.Yellow
    Else
        EmailTextBox.BackColor = Color.Green
    End If
End Sub