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Digitally Signed Email

I have the working code below for sending digitally signed emails. I need to insert an html-based signature with the gif logo, which needs to be extracted from the assembly resources. I googled around and found Convert.ToBase64String() as a possible solution, but Outlook does not display the image. The second approach would be a LinkedResource with AlternateView to embed my image, but in fact I was not able to get it to work with the code below. I already have AlternateView to send a digitally signed email. Is there any way to add an image?

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

 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 } }

EDIT: I had to re-open this thread as the previously accepted answer is not good enough.

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I think it is not possible to sign the entire message using System.Net.Mail . But it can also help you: - Send email in a C # tutorial - SSL, HTML, inline image, S / MIME

Also check the following: - ( Send email with embedded images - ImportHtml - Example ): -

 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); } } } }
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