Example

var client = new RestClient("https://app-x.nipamail.com/v1.0/transactional/post?accept_token=NPAPP-IGBmfucf0Np567WzwAH1KuRovnszt9r4HJPJ2U4SRhPk1pCeBXEi7nUkixLby8qwwwymbXwtV3gjOMeodNKlcAChYrZ0D8TQv60208fxXIZlJ7www");
client.Timeout = -1;
var request = new RestRequest(Method.POST);
request.AlwaysMultipartFormData = true;
request.AddParameter("from_name", "Thaksinai Kondee");
request.AddParameter("from_email", "thaksinai@hotmail.com");
request.AddParameter("to", "thaksinai@ispio.com");
request.AddParameter("subject", "ร่วมฉลอง ครบรอบการก่อตั้ง บริษัท Nipa technology วันนี้ เวลา 18:00 น.");
request.AddParameter("message", "content1");
request.AddParameter("reply_email", "se55660159@gmail.com");
request.AddParameter("reply_name", "Thakweb.com");
IRestResponse response = client.Execute(request);
Console.WriteLine(response.Content);