Implementing email classification based on header name and value

Hi 

I am trying to implement email classification in my android email application.

The classification will work as follows

1. User creates a new email through my application and set some classification (from the list of available classifications), when user will hit the send button i will add one custom header in the list of rfc822 headers something like below

x-email-classification: Public

or 

x-email-classification: Confidential

2. Similiarly, when a user will receive an email with some classification, i will parse the headers and find the classification type. So that when user replies to the classified email we can retain the classification.

Here comes my problem

I know headers can be only created via transport rules on exchange, when i create a custom header using my email application it gets removed by exchange. 

Problem is since user can choose the classification from email app, i cannot put any exchange transport rule because it needs flag and its value hardcoded which is not my use case. The x-header need to go with the email through application.

So here are my doubts

1. Is there a way i can create custom headers using my active sync email application and it wont be discarded by exchange so that recipient will be able to parse the already classified email by sender.

2. If above is not possible then can we create some rule with active sync protocol to retain headers? 

Also, i have seen Vmware boxer is doing the same thing but sadly ,i am not able to figure out the header part.

https://docs.vmware.com/en/VMware-AirWatch/9.3/vmware-airwatch-guides-93/GUID-AW93-AppConfigsBoxer.html#PolicyClassMarkings_Configuration_Value

Any hints/suggestions will be really appreciated. 

Thanks in advance