1、安装Nuget包MailKit，引用命名空间。
using MailKit.Net.Smtp; using MimeKit;
注意：引用MailKit对应最新版本
2、定义收发地址和标题
MimeMessage message = new MimeMessage();
MailboxAddress from = new MailboxAddress("Admin","admin@example.com");
message.From.Add(from);
MailboxAddress to = new MailboxAddress("User", "user@example.com");
message.To.Add(to);
message.Subject = "This is email subject";
注意：Admin,User分别对应发送接收邮箱前缀
3、编写内容
BodyBuilder bodyBuilder = new BodyBuilder(); bodyBuilder.HtmlBody = "<h1>Hello World!</h1>"; bodyBuilder.TextBody = "Hello World!";
message.Body = bodyBuilder.ToMessageBody();
注意：也可以自定义模板，插入图片等等。
4、连接SMTP服务器发送邮件
SmtpClient client = new SmtpClient();
client.Connect("smtp_address_here", port_here, true); //例如：smtp.exmail.qq.com，465
client.Authenticate("admin@example.com", "password")； //发送邮件的账户密码
client.Send(message);
client.Disconnect(true);
client.Dispose();
