Failure sending email through GMail using C#

Question

I am trying to send email, but I receive the following error:

An attempt was made to access a socket in a way forbidden by its access permissions 72.52.4.90:587

Code:

var mail = new MailMessage();
var client = new SmtpClient();
client.Port = 587;
client.Host = "smtp.gmail.com";
client.EnableSsl = true;
client.Timeout = 10000;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Credentials = new NetworkCredential("[email protected]", "password");

mail.From = new MailAddress("[email protected]");
mail.To.Add(new MailAddress("[email protected]"));
mail.BodyEncoding = UTF8Encoding.UTF8;
mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure; 
mail.Subject = "this is a test email.";
mail.Body = "this is my test email body";
client.Send(mail);

NOTE: This code is based on other questions and answers already here in StackOverflow. However, after an extensive search, it appears that no one else has experienced this particular issue so far. According to the other Q&A this code should be working.

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UPDATE: After being told that this was a duplicate I've modified my code to the following, however, I'm still getting the same error.

    private static void Main(string[] args)
    {
        var From = new MailAddress("[email protected]", "Me");
        var To = new MailAddress("[email protected]", "Me Too");
        var client = new SmtpClient
        {
            Host = "smtp.gmail.com",
            Port = 587, //25
            EnableSsl = true,
            DeliveryMethod = SmtpDeliveryMethod.Network,
            UseDefaultCredentials = false,
            Credentials = new NetworkCredential(From.Address, "password"),
            Timeout = 20000
        };

        using (var mail = new MailMessage(From, To)
        {
            Subject = @"this is a test email.",
            Body = @"this is my test email body"
        })
        {
            client.Send(mail);
        };
    }