dotnet-core_mail-server/MailServer/Mail.cs

using System;
using System.Collections.Generic;
using System.Text;

namespace MailServer
{
    public class Mail
    {
        public string From { get; private set; }
        public string To { get; private set; }

        public string Data { get; set; }

        public Mail(string from, string to, string data)
        {
            From = from;
            To = to;
            Data = data;
        }

        public string GetSenderDomain()
        {
            return From.Split('@')[1];
        }
    }
}