Message causes amavis to stop processing

[Alex]

Hi,
I've received a few messages today that have caused amavis to just get
stuck when it starts to process them, and no further messages are
processed until I stop amavis, delete the actual message from the
postfix queue, and the tmp directory that it was working with when it
choked.

I've created a copy of the message here:

http://pastebin.com/DJxcZctL

"mydomain.com" is my domain. Is it something in my configuration
causing this? Is it perhaps some mime type that it is trying to
process, but can't?

How do I debug this?

Thanks for any suggestions.
Alex