FluentMailSyntax.cs

using System;

namespace App
{
    class Program
    {
        private static void Main(string[] args)
        {
            MailTemplate
                .Configure
                    .With(mt => mt.To = "michaelameyaw7@gmail.com")
                    .With(mt => mt.From = "example@gmail.com")
                    .With(mt => mt.Subject = "Fluent syntax in CSharp")
                    .With(mt => mt.Body = "Hello, this is mail body")
                    .With(mt => mt.Attachement = "file.pdf")
               .Build();

            Console.ReadKey();
        }
    }

    public class MailTemplate
    {
        // regular auto properties
        public string To { get; set; }
        public string From { get; set; }
        public string Subject { get; set; }
        public string Body { get; set; }
        public string Attachement { get; set; }

        public static MailTemplate Configure { get => new MailTemplate(); }


        public MailTemplate With(Action<MailTemplate> func)
        {
            func(this);
            return this;
        }

        internal void Build()
        {
            Console.WriteLine("Sending the mail....");
        }
    }
}