I am working on an Outlook VSTO project where I need to display emails as HTML within a web form. However, images referenced by CID are not displaying correctly. To resolve this, I downloaded the images to temporary files.

The code works for images attached to the email but fails for images used in signatures. How can I ensure that all CID-referenced images, including those in signatures, are displayed correctly?
these are my methods to extract HTML body and save to the temp file

        public string EmailBodyToHtml(MailItem mi)
    {
        string htmlBody = mi.HTMLBody;
        var result = mi.HTMLBody;
        Regex reg = new Regex(@"<img[^>]*src=[""']cid:(?<cid>[^""']+)[""'][^>]*>");
        var matches = reg.Matches(htmlBody);
        foreach (Match match in matches)
        {
            string cid = match.Groups["cid"].Value;
            string tempFile = SaveInlineImageToTcempFile(mi, cid);
            if (!string.IsNullOrEmpty(tempFile))
            {
                result = result.Replace($"cid:{cid}", tempFile);
            }
        }
        return result;
    }

        private string SaveInlineImageToTcempFile(MailItem mi, string cid)
    {
        try
        {
            foreach (Attachment item in mi.Attachments)
            {
                PropertyAccessor pa = item.PropertyAccessor;
             string attCid=""+   pa.GetProperty("http://schemas.microsoft.com/mapi/proptag/0x3712001F") as string;
                if (attCid!=null && attCid.ToLower()==cid.ToLower())
                {
                    string tempFile = Path.Combine(Path.GetTempPath(), item.FileName);
                    item.SaveAsFile(tempFile);
                    return tempFile;
                }
            }
        }
        catch (System.Exception e)
        {
            var msg = e.Message;
           
        }
        return null;
    }

the error I’m getting the exception for signatures is “Cannot save the attachment. Cannot add the attachment; no data source was provided.”