1、 登录mailgun官网注册账号，并激活账号。
2、登录账号后进入查看 domain
上面的即是 mailgun默认给予免费测试的domain。
3、点击 domain name 查看域名信息，注意发邮件要用到
4、测试要发送的邮箱，必须要把 邮箱地址添加上mailgun中的Authorized Recipients 中否则会提示："Sandbox subdomains are for test purposes only. Please add your own domain or add the address to authorized recipients in Account Settings."
具体设置方法 点击mailgun的 Account Settings 把要测试的邮件添加到Recipients 中
5、实现代码 mailgun 中有（示例）
public static IRestResponse SendSimpleMessage(){RestClient client = new RestClient();client.BaseUrl = new Uri("/v3");client.Authenticator =new HttpBasicAuthenticator("api","key-f6dd9wewe32d2223345026e3d0423968a18ecb37ad1");RestRequest request = new RestRequest();request.AddParameter("domain", "", ParameterType.UrlSegment);request.Resource = "{domain}/messages";request.AddParameter("from", "postmaster@");request.AddParameter("to", "1787940846@");request.AddParameter("subject", "Hello");request.AddParameter("text", "Testing some Mailgun awesomness!");request.Method = Method.POST;return client.Execute(request);}
