When you need to display emails in browser controls and those emails contain images then you must convert email body to html and include images as BASE64 strings. This is shown here.
Use this Class as Mime message to HTML converter:
using MimeKit.Tnef;
using MimeKit;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
namespace Projektabrechnung.Services
{
/// <summary>
/// Visits a MimeMessage and generates HTML suitable to be rendered by a browser control.
/// </summary>
public class MimeMessageToHTMLConverter : MimeVisitor
{
List<MultipartRelated> stack = new List<MultipartRelated>();
List<MimeEntity> attachments = new List<MimeEntity>();
readonly string tempDir;
string body;
/// <summary>
/// Creates a new HtmlPreviewVisitor.
/// </summary>
/// <param name="tempDirectory">A temporary directory used for storing image files.</param>
public MimeMessageToHTMLConverter(string tempDirectory)
{
tempDir = tempDirectory;
}
/// <summary>
/// The list of attachments that were in the MimeMessage.
/// </summary>
public IList<MimeEntity> Attachments
{
get { return attachments; }
}
/// <summary>
/// The HTML string that can be set on the BrowserControl.
/// </summary>
public string HtmlBody
{
get { return body ?? string.Empty; }
}
protected override void VisitMultipartAlternative(MultipartAlternative alternative)
{
// walk the multipart/alternative children backwards from greatest level of faithfulness to the least faithful
for (int i = alternative.Count - 1; i >= 0 && body == null; i--)
alternative[i].Accept(this);
}
protected override void VisitMultipartRelated(MultipartRelated related)
{
var root = related.Root;
// push this multipart/related onto our stack
stack.Add(related);
// visit the root document
root.Accept(this);
// pop this multipart/related off our stack
stack.RemoveAt(stack.Count - 1);
}
// look up the image based on the img src url within our multipart/related stack
bool TryGetImage(string url, out MimePart image)
{
UriKind kind;
int index;
Uri uri;
if (Uri.IsWellFormedUriString(url, UriKind.Absolute))
kind = UriKind.Absolute;
else if (Uri.IsWellFormedUriString(url, UriKind.Relative))
kind = UriKind.Relative;
else
kind = UriKind.RelativeOrAbsolute;
try
{
uri = new Uri(url, kind);
}
catch
{
image = null;
return false;
}
for (int i = stack.Count - 1; i >= 0; i--)
{
if ((index = stack[i].IndexOf(uri)) == -1)
continue;
image = stack[i][index] as MimePart;
return image != null;
}
image = null;
return false;
}
// Save the image to our temp directory and return a "file://" url suitable for
// the browser control to load.
// Note: if you'd rather embed the image data into the HTML, you can construct a
// "data:" url instead.
/*string SaveImage(MimePart image, string url)
{
string fileName = url.Replace(':', '_').Replace('\\', '_').Replace('/', '_');
string path = Path.Combine(tempDir, fileName);
if (!File.Exists(path))
{
using (var output = File.Create(path))
image.Content.DecodeTo(output);
}
return "file://" + path.Replace('\\', '/');
}*/
string SaveImage(MimePart image, string url)
{
using (var output = new MemoryStream())
{
image.Content.DecodeTo(output);
var buffer = output.GetBuffer();
int length = (int)output.Length;
return string.Format("data:{0};base64,{1}", image.ContentType.MimeType, Convert.ToBase64String(buffer, 0, length));
}
}
// Replaces <img src=...> urls that refer to images embedded within the message with
// "file://" urls that the browser control will actually be able to load.
void HtmlTagCallback(HtmlTagContext ctx, HtmlWriter htmlWriter)
{
if (ctx.TagId == HtmlTagId.Image && !ctx.IsEndTag && stack.Count > 0)
{
ctx.WriteTag(htmlWriter, false);
// replace the src attribute with a file:// URL
foreach (var attribute in ctx.Attributes)
{
if (attribute.Id == HtmlAttributeId.Src)
{
MimePart image;
string url;
if (!TryGetImage(attribute.Value, out image))
{
htmlWriter.WriteAttribute(attribute);
continue;
}
url = SaveImage(image, attribute.Value);
htmlWriter.WriteAttributeName(attribute.Name);
htmlWriter.WriteAttributeValue(url);
}
else
{
htmlWriter.WriteAttribute(attribute);
}
}
}
else if (ctx.TagId == HtmlTagId.Body && !ctx.IsEndTag)
{
ctx.WriteTag(htmlWriter, false);
// add and/or replace oncontextmenu="return false;"
foreach (var attribute in ctx.Attributes)
{
if (attribute.Name.ToLowerInvariant() == "oncontextmenu")
continue;
htmlWriter.WriteAttribute(attribute);
}
htmlWriter.WriteAttribute("oncontextmenu", "return false;");
}
else
{
// pass the tag through to the output
ctx.WriteTag(htmlWriter, true);
}
}
protected override void VisitTextPart(TextPart entity)
{
TextConverter converter;
if (body != null)
{
// since we've already found the body, treat this as an attachment
attachments.Add(entity);
return;
}
if (entity.IsHtml)
{
converter = new HtmlToHtml
{
HtmlTagCallback = HtmlTagCallback
};
}
else if (entity.IsFlowed)
{
var flowed = new FlowedToHtml();
string delsp;
if (entity.ContentType.Parameters.TryGetValue("delsp", out delsp))
flowed.DeleteSpace = delsp.ToLowerInvariant() == "yes";
converter = flowed;
}
else
{
converter = new TextToHtml();
}
string text = entity.Text;
body = converter.Convert(entity.Text);
}
protected override void VisitTnefPart(TnefPart entity)
{
// extract any attachments in the MS-TNEF part
attachments.AddRange(entity.ExtractAttachments());
}
protected override void VisitMessagePart(MessagePart entity)
{
// treat message/rfc822 parts as attachments
attachments.Add(entity);
}
protected override void VisitMimePart(MimePart entity)
{
// realistically, if we've gotten this far, then we can treat this as an attachment
// even if the IsAttachment property is false.
attachments.Add(entity);
}
}
}
Then use this class as follows:
// Get email from Graph as eml stream. You can get this out of property "Content".
var emlstream = _appClient.Users[eMailReceiveJob.popUserName].Messages[message.Id].Content.Request().GetAsync().Result;
// Create a new MimeKit message and load eml stream
var mimeMessage = MimeMessage.Load(emlstream);
// Create new MimeMessageToHTMLConverter instance
var htmlConverter = new MimeMessageToHTMLConverter("");
// Convert message in HTML
mimeMessage.Accept(htmlConverter);
// Store HTML body
String = htmlConverter.HtmlBody;