Zend certified PHP/Magento developer

Thunderbird removes X-Headers

The title.

I have a central mail account which has only one purpose, forwarding all incoming mails to another email address. I want to pass information through X-Headers (apparently this is a thing). But Thunderbird removes those headers.

The only way I have now to pass information is through the subject or the body, but that is ugly. Any solution for this problem?