C# sending mails with images inline using SmtpClient

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("[email protected]"));
    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.

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