@mmccarn thanks for the info!
Coupled with what Jean advised, I've got a level 8 dump from the same sender, but I did not have time to sanitize and upload here. What's strange though is that this time there was no double sending of the file... Not sure why that happened, or whether I've missed the second, plaintext version of the message. Up to and including Wednesday I've got some pretty difficult days coming up.
But it will be a good thing to be able to help those guys fix their server: their organization is a NGO dealing with consumer allegations of company wrongdoings...