C# 带有数字签名和嵌入图像的电子邮件

我有以下发送数字签名电子邮件的工作代码。我必须插入一个带有gif徽标的基于html的签名，该签名应该从程序集资源中提取。我在谷歌上搜索了一下，找到了

Convert.ToBase64String（）

作为可能的解决方案，但Outlook没有显示图像。 第二种方法是使用

LinkedResource

和

AlternateView

来嵌入我的图像，但我实际上无法使用下面的代码。我已经有了一个

AlternateView

来发送带有数字签名的电子邮件。是否也可以以某种方式添加图像

So

mailer（to，from，from_name，relay，subject，body，cc1，cc2）

编辑：我必须重新打开此线程，因为以前接受的答案不够好。
我确实认为不可能使用
System.Net.Mail
对整个邮件进行签名。但这也可能对您有所帮助：-

同时检查以下内容：-（）：-

使用系统；
使用System.Collections.Generic；
使用系统文本；
使用电子邮件//添加EASendMail命名空间
命名空间mysendemail
{
班级计划
{
静态void Main（字符串[]参数）
{
SmtpMail-oMail=新的SmtpMail（“TryIt”）；
SmtpClient oSmtp=新的SmtpClient（）；
//设置发件人电子邮件地址，请将其更改为您的
oMail.From=”test@emailarchitect.net";
//设置收件人电子邮件地址，请将其更改为您的
oMail.To=”support@emailarchitect.net";
//设置电子邮件主题
oMail.Subject=“测试带有附件的html电子邮件”；
//您的SMTP服务器地址
SmtpServer oServer=新的SmtpServer（“smtp.emailarchitect.net”）；
//ESMTP身份验证的用户和密码（如果服务器不需要）
//用户身份验证，请删除以下代码。
oServer.User=”test@emailarchitect.net";
oServer.Password=“testpassword”；
//如果您的SMTP服务器需要SSL连接，请添加此行
//oServer.ConnectType=SmtpConnectType.ConnectSSLAuto；
尝试
{
//导入html正文，并将链接图像作为嵌入图像导入。
oMail.ImportHtml（“测试导入TML”，
“c:\\my picture”//test.gif位于c:\\my picture中
ImportHtmlBodyOptions.ImportLocalPictures | ImportHtmlBodyOptions.ImportCS）；
Console.WriteLine（“开始发送带有嵌入图像的电子邮件…”）；
SendMail（oServer，oMail）；
Console.WriteLine（“电子邮件已成功发送！”）；
}
捕获（异常ep）
{
Console.WriteLine（“发送电子邮件失败，错误如下：”）；
控制台写入线（ep消息）；
}
}
}
}

private void mailer(string toaddress, string fromaddress, string fromaddress_disp, string relays, string mailsubject, string bodytext, string ccman, string cccct)
{
    string certname = "";

    MailAddress from = new MailAddress(fromaddress, fromaddress_disp);
    MailAddress to = new MailAddress(toaddress);
    MailAddress cc_man = new MailAddress(ccman);
    MailAddress cc_cct = new MailAddress(cccct);
    MailMessage message = new MailMessage(from, to);
    message.CC.Add(cc_man);
    message.CC.Add(cc_cct);
    message.Subject = mailsubject;
    message.IsBodyHtml = true;
    string body = "Content-Type: text/html; charset=iso-8859-1 \r\nContent-Transfer-Encoding: 8bit\r\n\r\n" + bodytext;
    byte[] messageData = Encoding.ASCII.GetBytes(body);
    ContentInfo content = new ContentInfo(messageData);

    SignedCms Cms = new SignedCms(new ContentInfo(messageData));
    X509Store store = new X509Store(StoreLocation.CurrentUser);
    store.Open(OpenFlags.ReadOnly);

    RSACryptoServiceProvider csp = null;
    X509Certificate2Collection certCollection = store.Certificates;
    X509Certificate2 cert = null;
    foreach (X509Certificate2 c in certCollection)
    {
        if ((c.Subject.Contains("myEmailAddress")) && (c.FriendlyName.Contains("CompanyEmailDigSig")))
        {
            cert = c;
            break;
        }
    }

    if (cert != null)
    {
            csp = (RSACryptoServiceProvider)cert.PrivateKey;
    }
    else
    {
        throw new Exception("Valid certificate was not found");
    }

    CmsSigner Signer = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, cert);
    Cms.ComputeSignature(Signer);
    byte[] SignedBytes = Cms.Encode();
    MemoryStream signedStream = new MemoryStream(SignedBytes);
    AlternateView signedView = new AlternateView(signedStream, "application/pkcs7-mime; smime-type=signed-data; name=sig.p7m");
    message.AlternateViews.Add(signedView);
    SmtpClient client = new SmtpClient(relays);
    store.Close();

    try
    {
        client.Send(message);
    }
    catch (Exception ex)
    {
    //exception
    }
}

using System;
using System.Collections.Generic;
using System.Text;
using EASendMail; //add EASendMail namespace

namespace mysendemail
{
    class Program
    {
        static void Main(string[] args)
        {
            SmtpMail oMail = new SmtpMail("TryIt");
            SmtpClient oSmtp = new SmtpClient();

            // Set sender email address, please change it to yours
            oMail.From = "test@emailarchitect.net";

            // Set recipient email address, please change it to yours
            oMail.To = "support@emailarchitect.net";

            // Set email subject
            oMail.Subject = "test html email with attachment";

            // Your SMTP server address
            SmtpServer oServer = new SmtpServer("smtp.emailarchitect.net");

            // User and password for ESMTP authentication, if your server doesn't require
            // User authentication, please remove the following codes.            
            oServer.User = "test@emailarchitect.net";
            oServer.Password = "testpassword";

            // If your SMTP server requires SSL connection, please add this line
            // oServer.ConnectType = SmtpConnectType.ConnectSSLAuto;

            try
            {
               // Import html body and also import linked image as embedded images.
               oMail.ImportHtml( "<html><body>test <img src=\"test.gif\"> importhtml</body></html>",
                    "c:\\my picture", //test.gif is in c:\\my picture
                    ImportHtmlBodyOptions.ImportLocalPictures | ImportHtmlBodyOptions.ImportCss );

                Console.WriteLine("start to send email with embedded image...");
                oSmtp.SendMail(oServer, oMail);
                Console.WriteLine("email was sent successfully!");
            }
            catch (Exception ep)
            {
                Console.WriteLine("failed to send email with the following error:");
                Console.WriteLine(ep.Message);
            }
        }
    }
}