title: PDF attachments are changing to unusable DAT files
body: <p>I have an system that is an in house solution attempting to email invoices to clients. This system works great except for one client gets .dat files instead of the nicely generated .pdf files that everyone else gets. </p>
  
  <p>I have researched the problem and many things point to issues with Outlook sending emails(not using outlook) and splitting the files because it is to large(it isn't, we can manualy send the email fine.)</p>
  
  <p>The files get renamed to something like "=_utf-8_B_Q29uc29saWRhdGVkIEludm9pY2VzIGZv.dat" instead of "1180426.pdf".</p>
  
  <p>After the headers on both files is just lines of characters that don't mean anything to me.</p>
  
  <p>the headers of the .dat files:
  file1</p>
  
  <pre><code> =?utf-8?B?Y2lCQmJIQm9ZU0JKYm5OMWJHRjBhVzl1Pz0NCiA9P3V0Zi04P0I/SUNZ?=\
  \
  
   =?utf-8?B?Z1YyRjBaWEp3Y205dlptbHVaeUF0SUVGc2NHaGhJRWx1YzNWc1lYUnBi?=\
  \
  
   =?utf-8?B?MjRnSmlCWFlYUmw/PQ0KID0/dXRmLTg/Qj9jbkJ5YjI5bWFXNW5JT0tB?=\
  \
  
   =?utf-8?B?a3lCVmJtbDJaWEp6WVd3Z1EybDBlU3dnS0RJd01USXRNRFF0TVRNcD89?=\
  \
   =?utf-8?B?DQogPT91dGYtOD9CP0xuQmtaZz09Pz0=?="
  Content-Transfer-Encoding: base64
  Content-Disposition: attachment
  </code></pre>
  
  <p>file2</p>
  
  <pre><code> =?utf-8?B?YUdFZ1NXNXpkV3hoZEdsdmJpQW1JRmRoPz0NCiA9P3V0Zi04P0I/ZEdW?=\
  \
  
   =?utf-8?B?eWNISnZiMlpwYm1jZ0xTQkJiSEJvWVNCSmJuTjFiR0YwYVc5dUlDWWdW?=\
  \
  
   =?utf-8?B?MkYwWlhKd2NtOXY/PQ0KID0/dXRmLTg/Qj9abWx1WnlEaWdKTWdWVzVw?=\
  \
  
   =?utf-8?B?ZG1WeWMyRnNJRU5wZEhrc0lDZ3lNREV5TFRBMExURXpLUzV3WkdZPT89?=\
  \
   =?utf-8?B??="
  Content-Transfer-Encoding: base64
  Content-Disposition: attachment
  </code></pre>
  
  <p>Does anyone have any idea on why this is happening?</p>