Unsupported mimetype: message/rfc822

[bamthomas]

When loading the preview of an email we have this exception :

2019-09-18 16:35:28,821 ERROR [waitress:363][waitress] Exception while serving /api/v1/thumbnail/local-datashare/90637e2a7211900a9d1006a7198da70c9d3d814e61fc7bed833eb177e20e67794673ef85bce77d704f5bf58924bd7d03
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/pyramid/tweens.py", line 13, in _error_handler
    response = request.invoke_exception_view(exc_info)
  File "/usr/local/lib/python3.7/site-packages/pyramid/view.py", line 769, in invoke_exception_view
    raise HTTPNotFound
pyramid.httpexceptions.HTTPNotFound: The resource could not be found.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/waitress/channel.py", line 356, in service
    task.service()
  File "/usr/local/lib/python3.7/site-packages/waitress/task.py", line 172, in service
    self.execute()
  File "/usr/local/lib/python3.7/site-packages/waitress/task.py", line 440, in execute
    app_iter = self.channel.server.application(environ, start_response)
  File "/usr/local/lib/python3.7/site-packages/pyramid/router.py", line 270, in __call__
    response = self.execution_policy(environ, self)
  File "/usr/local/lib/python3.7/site-packages/pyramid/router.py", line 279, in default_execution_policy
    return request.invoke_exception_view(reraise=True)
  File "/usr/local/lib/python3.7/site-packages/pyramid/view.py", line 768, in invoke_exception_view
    reraise_(*exc_info)
  File "/usr/local/lib/python3.7/site-packages/pyramid/compat.py", line 179, in reraise
    raise value
  File "/usr/local/lib/python3.7/site-packages/pyramid/router.py", line 277, in default_execution_policy
    return router.invoke_request(request)
  File "/usr/local/lib/python3.7/site-packages/pyramid/router.py", line 249, in invoke_request
    response = handle_request(request)
  File "/usr/local/lib/python3.7/site-packages/pyramid/tweens.py", line 43, in excview_tween
    response = _error_handler(request, exc)
  File "/usr/local/lib/python3.7/site-packages/pyramid/tweens.py", line 17, in _error_handler
    reraise(*exc_info)
  File "/usr/local/lib/python3.7/site-packages/pyramid/compat.py", line 179, in reraise
    raise value
  File "/usr/local/lib/python3.7/site-packages/pyramid/tweens.py", line 41, in excview_tween
    response = handler(request)
  File "/usr/local/lib/python3.7/site-packages/pyramid/router.py", line 148, in handle_request
    registry, request, context, context_iface, view_name
  File "/usr/local/lib/python3.7/site-packages/pyramid/view.py", line 657, in _call_view
    response = view_callable(context, request)
  File "/usr/local/lib/python3.7/site-packages/pyramid/viewderivers.py", line 401, in viewresult_to_response
    result = view(context, request)
  File "/usr/local/lib/python3.7/site-packages/pyramid/viewderivers.py", line 144, in _requestonly_view
    response = view(request)
  File "/usr/local/lib/python3.7/site-packages/dspreview/views.py", line 61, in thumbnail
    return FileResponse(get_jpeg_preview(params), content_type='image/jpeg')
  File "/usr/local/lib/python3.7/site-packages/dspreview/preview.py", line 15, in get_jpeg_preview
    return manager.get_jpeg_preview(**params)
  File "/usr/local/lib/python3.7/site-packages/preview_generator/manager.py", line 156, in get_jpeg_preview
    builder = self._factory.get_preview_builder(mimetype)
  File "/usr/local/lib/python3.7/site-packages/preview_generator/preview/builder_factory.py", line 49, in get_preview_builder
    raise UnsupportedMimeType("Unsupported mimetype: {}".format(mimetype))
preview_generator.exception.UnsupportedMimeType: Unsupported mimetype: message/rfc822