Mail reply headers remove

[Jorge Alvaro]

Hi,

I'm building an application that will receive some mails and reply to
them. I've been trying to set the headers used by mail applications to
diplay threaded conversations but it looks like App Engine (Java,
1.4.0) is removing them.

I'm trying to set "In-Reply-To" and "References" headers but none of
them are received for the response.

I've found this related issue:
http://code.google.com/p/googleappengine/issues/detail?id=2802

But I'm already using MimeMessage's msg.reply(false) and setting the
headers.

Has anyone solved this problem to get replies in the same thread
conversation?
Any plan to allow these headers?
Any list of allowed/forbidden headers?

Thanks!
Jorge