From: Arnt Gulbrandsen <arnt@example.com>
To: Arnt Gulbrandsen <arnt@example.com>
Date: Thu, 20 May 2004 14:28:51 +0200
Content-Disposition: attachment; filename="blåbærsyltetøy"
Content-Type: text/plain; format=flowed
Mime-Version: 1.0

It's a bit odd that a single-part message is an attachment with a 
filename. But perfectly legal.