Header firewall shouldn't apply in internal organisation

Hello, 

I am working on email application for exchange and some feature required to add x header to the email.

Something like below

X-test-header: my header

X-test-header2: my header 2

When i send the email with following header along with the list of other headers i don't see that on the recipient side's inbox.

The recipient is in the same organisation, so i dont think header firewal might be problem here.

Clearly i am missing something. Can you help me please.

Thanks in advance