C# 发送邮件（带有附件）

当前所用框架（.NET 5.0）

引用Nuget包：MailKit（3.2.0）、MimeKit（3.2.0）

using MailKit.Security;
using MimeKit;
using System;
using System.Net.Mime;

namespace Mailbox
{
    internal class Program
    {
        static void Main(string[] args)
        {
            QQEmail email = new QQEmail();
            email.AddFile(@"F:\Kyson\其他文件\Mailbox\Mailbox\images\1.jpg", "1.jpg");
            string html = "<p>我是邮件文字/html内容</p>";
            email.Send("主题:测试发送邮件", "[email protected]", "[email protected]", html);
        }
    }

    public class QQEmail
    {
        Multipart multipart = new Multipart("mixed");
        /// <summary>
        /// 添加文件
        /// </summary>
        /// <param name="file"></param>
        /// <param name="name"></param>
        public bool AddFile(string file, string name)
        {
            if (!System.IO.File.Exists(file))
            {
                return false;
            }
            try
            {
                System.IO.FileStream fs = new System.IO.FileStream(file, System.IO.FileMode.Open, System.IO.FileAccess.Read, System.IO.FileShare.ReadWrite);

                //附件
                var attimg = new MimePart(MediaTypeNames.Application.Octet)
                {
                    Content = new MimeContent(fs, ContentEncoding.Default),
                    ContentDisposition = new MimeKit.ContentDisposition(MimeKit.ContentDisposition.Attachment),
                    ContentTransferEncoding = ContentEncoding.Default,
                    FileName = name,
                    IsAttachment = true,
                };
                multipart.Add(attimg);
                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }

        /// <summary>
        /// 发送
        /// </summary>
        /// <param name="subject">主题</param>
        /// <param name="from">发送人</param>
        /// <param name="to">接收人</param>
        /// <param name="html">邮件内容支持html</param>
        /// <returns></returns>
        public string Send(string subject, string from, string to, string html)
        {
            using (var smtp = new MailKit.Net.Smtp.SmtpClient())
            {
                MimeMessage mail = new MimeMessage();
                mail.From.Add(new MailboxAddress("Yuan天空", from));
                mail.To.Add(new MailboxAddress(to, to));
                mail.Subject = subject;
                if (string.IsNullOrEmpty(html))
                {
                    return "发送内容不能为空";
                }

                var Html = new TextPart(MimeKit.Text.TextFormat.Html)
                {
                    Text = html
                };
                multipart.Add(Html);
                mail.Body = multipart;

                smtp.ServerCertificateValidationCallback = (s, c, h, e) => true;
                //连接邮箱服务器 
                //!!!需要注意的是阿里云服务器默认是禁止25端口的,安全组添加也不行需要提交阿里云审核才能开通 ,  这里使用587端口是可以发送的(服务器实测发送延迟很高 ,本地调试发送挺快, 不知道是不是服务器配置比较低的原因)
                smtp.Connect("smtp.qq.com", 587, SecureSocketOptions.None);
                //登录认证 qq邮箱账号和授权密钥
                smtp.Authenticate("[email protected]", "xxxx");
                smtp.Timeout = 600000;
                string res = smtp.Send(mail);
                smtp.Disconnect(true);
                return res;
            }
        }
    }
}