gistfile1.cs

using System.Net;
using System.IO;
using System.Collections;
using System.Collections.Specialized;
using System;
using System.Web;
using System.Security.Cryptography.X509Certificates;

public class Program : ICertificatePolicy {
	public bool CheckValidationResult (ServicePoint sp, X509Certificate certificate, WebRequest request, int error) {
		return true;
	}
	
	public static void Main(string[] args)  {
		ServicePointManager.CertificatePolicy = new Program ();
		using(WebClient client = new WebClient()) {
			NameValueCollection postParams = new NameValueCollection();
			postParams["username"] = "myemail@test.com";
			postParams["api_key"] = "**********";
			postParams["other_value"] = "asdasd";
			
			client.UploadData("https://madmimi.com/mailers", "POST", 
								System.Text.Encoding.UTF8.GetBytes(Program.ConvertNVCToQueryString(postParams)));
		}
	}
	
	public static String ConvertNVCToQueryString(NameValueCollection paramsNVC) {
		string[] pairs = new string[paramsNVC.Keys.Count];

		for(int i = 0; i < paramsNVC.Keys.Count; i++) {
			string key = paramsNVC.Keys.Get(i);
			string value = paramsNVC[key];
			pairs[i] = String.Concat(key, "=", HttpUtility.UrlEncode(value));
		}
		
		return String.Join("&", pairs);
	}
}