private void button1_Click(object sender, EventArgs e)
{
EnvioDeMail enviar_mail = new EnvioDeMail();
//De tipo formulario Form
enviar_mail.ShowDialog();
}
//Formulario de enviar mail
private void optionsToolStripMenuItem_Click(object sender, EventArgs e)
{
EnvioDeMail envioDeMail = new EnvioDeMail();
envioDeMail.MdiParent = this;
envioDeMail.Show();
//envioDeMail.ShowDialog();
}