Sending email with C# to display in iOS

Question

I am trying to send am email from a C# SharePoint application that includes custom styles and attachments. It uses a template structure and I have successfully configured the email to use the new styles and attachments for inline images and it displays fine for Outlook clients. However, when I try to view the email on an iOS device, I seeing the images twice; once inline and once again at the end of the email.

The closest I could find to a solution was written for Django and I haven't had much success porting that solution to C#. I found that answer here: Displaying inline images on iPhone, iPad

I configure the attachments in this way:

System.Net.Mail.Attachment attachment = new System.Net.Mail.Attachment(new MemoryStream(imageBytes.Key), MediaTypeNames.Image.Jpeg);
attachment.Name = imageBytes.Value;
attachment.ContentDisposition.Inline = true;
attachment.ContentId = imageBytes.Value;

attachments.Add(attachment);

How can I go about displaying these images only once? I need to be able to display them in such a way that they are only displayed inline. I am not sure if this means I should use alternative views and if so, how to go about using them.

EDIT:

Here is the remainder of the code that I use to generate the emails:

public override System.Net.Mail.MailMessage GenerateMessage()
{
var keys = new Dictionary<string, string>();
var fileBytes = new Dictionary<byte[], string>();
var attachments = new List<System.Net.Mail.Attachment>();

var message = new MailMessage();

//get the attachment images as html in a dictionary object, byte[] and string   
fileBytes = GetEmailAttachments();

foreach (var imageBytes in fileBytes)
{
    System.Net.Mail.Attachment attachment = new System.Net.Mail.Attachment(new MemoryStream(imageBytes.Key), MediaTypeNames.Image.Jpeg);
    attachment.Name = imageBytes.Value;
    attachment.ContentDisposition.Inline = true;
    attachment.ContentId = imageBytes.Value;

    attachments.Add(attachment);
}

foreach (var attachment in attachments)
{
    message.Attachments.Add(attachment);
    string fileName = attachment.Name.Split('.')[0];

    switch (fileName)
    {
        case "img-approve":
            keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' alt={2} title={3}></a>", 
                innerMsg, attachment.ContentId, fileName, "test"));
            break;
        case "img-reject":
            keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' alt={2} title={3}></a>", 
                innerMsg1, attachment.ContentId, fileName, "test"));
            break;
        case "img-buyer":
            keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' height=100 alt=picture></a>", imageURL, attachment.ContentId));
            break;
        case "img-env":
            keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
            break;
        case "img-computer":
            keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
            break;
        case "logo":
            keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
            break;
        default:
            keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1}>", attachment.ContentId, fileName));
            break;
    }
}

//get the additional keys specific to this email
GenerateAdditionalKeys(keys, message);

//build the email
var body = ReplaceTemplateKeys(keys, _template);

if(!string.IsNullOrEmpty(toEmail))
{
    message.To.Add(toEmail);
}
if (!string.IsNullOrEmpty(ccEmail))
{
    message.CC.Add(ccEmail);
}

message.IsBodyHtml = true;
message.Body = body;

return message;
}

Answer 1

So, I think I found out what my problem was. What I did was a combination of many other solutions. Instead of attaching the files as Attachments, I created an alternate view and attached the files as LinkedResources. It looked a lot like the link that @Adriano supplied in the comment above, but what I had to make sure and do was to stop trying to use both Attachments and LinkedResources. Once I stopped relying on the Attachments to supply the ContentID used in the markup, everything works as expected. The code I got to work is below (I left the commented out parts for clarity of what was changed):

public override System.Net.Mail.MailMessage GenerateMessage()
{
var keys = new Dictionary<string, string>();
var fileBytes = new Dictionary<byte[], string>();
var attachments = new List<System.Net.Mail.Attachment>();

var message = new MailMessage();

//get the attachment images as html in a dictionary object, byte[] and string   
fileBytes = GetEmailAttachments();

var resourceList = new List<LinkedResource>();

foreach (var imageBytes in fileBytes)
{
System.Net.Mail.Attachment attachment = new System.Net.Mail.Attachment(new MemoryStream(imageBytes.Key), MediaTypeNames.Image.Jpeg);
attachment.Name = imageBytes.Value;
attachment.ContentDisposition.Inline = true;
attachment.ContentId = imageBytes.Value;

//attachments.Add(attachment);

var stream = new MemoryStream(imageBytes.Key);
var newResource = new LinkedResource(stream, "image/jpeg");
newResource.TransferEncoding = TransferEncoding.Base64;
newResource.ContentId = imageBytes.Value;
resourceList.Add(newResource);
}

foreach (var attachment in resourceList)
{
//message.Attachments.Add(attachment);
//string fileName = attachment.Name.Split('.')[0];

string fileName = attachment.ContentId.Split('.')[0];

switch (fileName)
{
    case "img-approve":
        keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' alt={2} title={3}></a>", 
            innerMsg, attachment.ContentId, fileName, "test"));
        break;
    case "img-reject":
        keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' alt={2} title={3}></a>", 
            innerMsg1, attachment.ContentId, fileName, "test"));
        break;
    case "img-buyer":
        keys.Add(fileName, String.Format("<a href={0} target=_top><img src='cid:{1}' height=100 alt=picture></a>", imageURL, attachment.ContentId));
        break;
    case "img-env":
        keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
        break;
    case "img-computer":
        keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
        break;
    case "logo":
        keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1} style=vertical-aign: middle>", attachment.ContentId, "test"));
        break;
    default:
        keys.Add(fileName, String.Format("<img src='cid:{0}' alt={1}>", attachment.ContentId, fileName));
        break;
}
}

//get the additional keys specific to this email
GenerateAdditionalKeys(keys, message);

//build the email
var body = ReplaceTemplateKeys(keys, _template);

if(!string.IsNullOrEmpty(toEmail))
{
    message.To.Add(toEmail);
}
if (!string.IsNullOrEmpty(ccEmail))
{
    message.CC.Add(ccEmail);
}

message.IsBodyHtml = true;
//message.Body = body;

return message;
}