How to send transactional e-mail messages from a ASP.NET C# web application using Twilio SendGrid API

You can send the mail by SDK of SendGrid.

var apiKey = Environment.GetEnvironmentVariable("NAME_OF_THE_ENVIRONMENT_VARIABLE_FOR_YOUR_SENDGRID_KEY");
var client = new SendGridClient(apiKey);
var from = new EmailAddress("test@example.com", "Example User");
var subject = "Sending with Twilio SendGrid is Fun";
var to = new EmailAddress("test@example.com", "Example User");
var plainTextContent = "and easy to do anywhere, even with C#";
var htmlContent = "<strong>and easy to do anywhere, even with C#</strong>";
var msg = MailHelper.CreateSingleEmail(from, to, subject, plainTextContent, htmlContent);
var response = await client.SendEmailAsync(msg);

You can get the full information from here: https://github.com/sendgrid/sendgrid-csharp#quick-start