Message resource extensions - Can be reviewed within the email itself?

I'm using Graph SDK in order to edit some Message resource properties. 

I'm adding an Extension using POST /users/{id}/messages/{id}/extensions endpoint.

How can I view the Extensions I added from within the email itself? (not by Graph SDK or Graph Explorer. The actual mail).

If it's not possible, storing the data on singleValueExtendedProperties / multiValueExtendedProperties will be reflected in the email itself?

Thanks.

Mor.