System.Net.Mail.MailMessage mailMessage = new System.Net.Mail.MailMessage();      
    mailMessage.From="发送者邮箱";      
    mailMessage.To.Add("收件人邮件列表");      
    mailMessage.CC.Add("抄送人邮件列表");      
    mailMessage.Subject = subject;      
    AlternateView htmlBody = AlternateView.CreateAlternateViewFromString(content,null,"text/html");//这里的content为邮件内容,内含图片相对路径,有时有多张图片
    LinkedResource lrImage = new LinkedResource("a.jpg","image/gif");      
    lrImage.ContentId = "Email001";      
    htmlBody.LinkedResources.Add(lrImage);      
    mailMessage.AlternateViews.Add(htmlBody);      
    SmtpClient.Send(mailMessage);     

LinkedResource lrImage = new LinkedResource("a.jpg","image/gif");