title: Unicode characters disappear in mail attachment name
body: <p>I develop an app, which needs to send zipped files via e-mail (in attachments). Everything is good  except one thing: cyrillic (or other unicode) characters in attachment name dissappears. They work fine in message name and message body, but not in attachment.</p>
  
  <p>I use following code for attachment:</p>
  
  <pre><code>var attachment = new Attachment(file, MediaTypeNames.Application.Zip);
  
  ContentDisposition disposition = attachment.ContentDisposition;
  
  disposition.CreationDate = File.GetCreationTime(file);
  disposition.ModificationDate = File.GetLastWriteTime(file);
  disposition.ReadDate = File.GetLastAccessTime(file);
  disposition.FileName = Path.GetFileName(file);            
  disposition.Size = new FileInfo(file).Length;
  disposition.DispositionType = DispositionTypeNames.Attachment;            
  message.Attachments.Add(attachment);
  smtpClient.Send(message);
  </code></pre>
  
  <p>And use SmtpClient Class to send E-mail. I tried some workarounds found on SO, like </p>
  
  <pre><code>att.Name = "история-болезни.doc";  // non-english filename    
  att.Name = System.Web.HttpUtility.UrlEncode(att.Name, System.Text.Encoding.UTF8);
  </code></pre>
  
  <p>But got nothing... My logs says that e-mail goes to server with correct attachment names and i also tried to send such an e-mail manually (not programmatically) and it also worked good.</p>
  
  <p>So, how can i workaround this problem? I found some patch for .Net framework, but it's not good for because i have to publish my app to many different clients and i don't want to install patches on their computer before the app can work properly.</p>
  
  <p><strong>UPD.</strong>
  <img src="https://i.stack.imgur.com/NJlYy.png" alt="Letter Sample (In Outlook)"></p>