Adding custom x-header to email

Hi 

I am working on an mobile email application, which uses active sync protocol. I am trying to add some custom email header in an email sent from the application something like below

x-classification-marking: red

x-custom-marking: my custom flag

Problem is i am adding these headers in the header list when sending the email and when checking inbox i can see these headers are clearly visible but on the recipient side i don't see the headers, i need the x-headers on the recipient side so that i can do some preprocessing but somehow i dont see it. 

Is there something i am missing ? The sender and recipient are in the same org so i dont think header firewall is blocking it.

Thanks in advance for help!