C# sending mails with images inline using SmtpClient

Question

SmtpClient() allows you to add attachments to your mails, but what if you wanna make an image appear when the mail opens, instead of attaching it?

As I remember, it can be done with about 4 lines of code, but I don't remember how and I can't find it on the MSDN site.

EDIT: I'm not using a website or anything, not even an IP address. The image(s) are located on a harddrive. When sent, they should be part of the mail. So, I guess I might wanna use an tag... but I'm not too sure, since my computer isn't broadcasting.

Answer 1

One solution that is often mentioned is to add the image as an Attachment to the mail, and then reference it in the HTML mailbody using a cid: reference.

However if you use the LinkedResources collection instead, the inline images will still appear just fine, but don't show as additional attachments to the mail. That's what we want to happen, so that's what I do here:

using (var client = new SmtpClient())
{
    MailMessage newMail = new MailMessage();
    newMail.To.Add(new MailAddress("you@your.address"));
    newMail.Subject = "Test Subject";
    newMail.IsBodyHtml = true;

    var inlineLogo = new LinkedResource(Server.MapPath("~/Path/To/YourImage.png"), "image/png");
    inlineLogo.ContentId = Guid.NewGuid().ToString();

    string body = string.Format(@"
            <p>Lorum Ipsum Blah Blah</p>
            <img src=""cid:{0}"" />
            <p>Lorum Ipsum Blah Blah</p>
        ", inlineLogo.ContentId);

    var view = AlternateView.CreateAlternateViewFromString(body, null, "text/html");
    view.LinkedResources.Add(inlineLogo);
    newMail.AlternateViews.Add(view);

    client.Send(newMail);
}

NOTE: This solution adds an AlternateView to your MailMessage of type text/html. For completeness, you should also add an AlternateView of type text/plain, containing a plain text version of the email for non-HTML mail clients.

Answer 2

The HTML Email and the images are attachments so it's just a case of referring to the image(s) by their content ids, i.e.

    Dim A As System.Net.Mail.Attachment = New System.Net.Mail.Attachment(txtImagePath.Text)
    Dim RGen As Random = New Random()
    A.ContentId = RGen.Next(100000, 9999999).ToString()
    EM.Body = "<img src='cid:" + A.ContentId +"'>" 

There seems to be comprehensive examples here: Send Email with inline images

Answer 3

When you say 4 lines of code, are you referring to this?

System.Net.Mail.Attachment inline = new System.Net.Mail.Attachment(@"imagepath\filename.png");
inline.ContentDisposition.Inline = true;

Answer 4

What about converting images in Base64 strings? AFAIK this can be easily embedded within mail body.

Take a look here.

Answer 5

The solution already posted is the best I have found, I'm just going to complete it with for example if you have multiple images.

        string startupPath = AppDomain.CurrentDomain.RelativeSearchPath;
        string path = Path.Combine(startupPath, "HtmlTemplates", "NotifyTemplate.html");
        string body = File.ReadAllText(path);

        //General tags replacement.
        body = body.Replace("[NOMBRE_COMPLETO]", request.ToName);
        body = body.Replace("[ASUNTO_MENSAJE]", request.Subject);

        //Image List Used to replace into the template.
        string[] imagesList = { "h1.gif", "left.gif", "right.gif", "tw.gif", "fb.gif" };

        //Here we create link resources one for each image. 
        //Also the MIME type is obtained from the image name and not hardcoded.
        List<LinkedResource> imgResourceList = new List<LinkedResource>();
        foreach (var img in imagesList)
        {
            string imagePath = Path.Combine(startupPath, "Images", img);
            var image = new LinkedResource(imagePath, "image/" + img.Split('.')[1]);
            image.ContentId = Guid.NewGuid().ToString();
            image.ContentType.Name = img;
            imgResourceList.Add(image);
            body = body.Replace("{" + Array.IndexOf(imagesList, img) + "}", image.ContentId);
        }

        //Altern view for managing images and html text is created.
        var view = AlternateView.CreateAlternateViewFromString(body, null, "text/html");
        //You need to add one by one each link resource to the created view
        foreach (var imgResorce in imgResourceList)
        {
            view.LinkedResources.Add(imgResorce);
        }

        ThreadPool.QueueUserWorkItem(o =>
        {
            using (SmtpClient smtpClient = new SmtpClient(servidor, Puerto))
            {
                smtpClient.EnableSsl = true;
                smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
                smtpClient.Timeout = 50000;
                smtpClient.UseDefaultCredentials = false;
                smtpClient.Credentials = new System.Net.NetworkCredential()
                {
                    UserName = UMail,
                    Password = password
                };
                using (MailMessage mailMessage = new MailMessage())
                {
                    mailMessage.IsBodyHtml = true;
                    mailMessage.From = new MailAddress(UMail);
                    mailMessage.To.Add(request.ToEmail);
                    mailMessage.Subject = "[NAPNYL] " + request.Subject;
                    mailMessage.AlternateViews.Add(view);
                    smtpClient.Send(mailMessage);
                }
            }
        });

As you can see you have an array of image names, it is important that the images are in the same folder because it is pointing to the same output folder.

Finally the email is sent as async so the user doesn't have to wait for it to be sent.

Answer 6

The process of making an image appear on the client when the mail is opened is a client function. As long as the client knows how to render the image & has not blocked any image content it will open it right away. You do not have to do anything special while sending the email to make it open on the client as long as you have correctly specified the image mime attachment type.