Hi Cédric:

Do you have a test for this? It looks like a testcase added to:

  class HeaderRoundupMessageTests(TestCase):

of test/test_mailgw_roundupmessage.py is the right place to put it.

I spent about 1/2 an hour trying to get a test put together from
your description but I didn't get a quoted printable subject
encoding to fail.

Re rolling back the patch for issue2551008, it doesn't look like
we have a valid test/tests for that case so I am uncomfortable
with unrolling that patch. IIUC that patch and this patch would be 
compatible so nothing bad would happen if it is not rolled back.

-- rouilj