Send a mail message via Mailgun using HttpClient

MailgunTest.cs

using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

[TestFixture]
public class MyClass
{
    const string DOMAIN = "samples.mailgun.org";
    const string API_KEY = "key-...";

    [Test]
    public void Test1()
    {
        Test1Async().Wait();
    }

    public async Task Test1Async()
    {
        var client = new HttpClient();
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", Convert.ToBase64String(UTF8Encoding.UTF8.GetBytes("api" + ":" + API_KEY)));


        var form = new Dictionary<string, string>();
        form["from"]    = "from@example.com";
        form["to"]      = "to@example.org";
        form["subject"] = "Test";
        form["text"]    = "testing testing...";

        var response = await client.PostAsync("https://api.mailgun.net/v2/" + DOMAIN + "/messages", new FormUrlEncodedContent(form));

        if (response.StatusCode == HttpStatusCode.OK)
        {
            Debug.WriteLine("Success");
        }
        else
        {
            Debug.WriteLine("StatusCode: " + response.StatusCode);
            Debug.WriteLine("ReasonPhrase: " + response.ReasonPhrase);
        }
    }
}