[Dovecot] Get some headers Variables

Hello Everyone again !!

I'm putting more functions in my plugin, and would need to access a value of one variable that is going to put in the header, how can I get this value by dovecot?

example, I have the header: X-ThereisMy: yes

How can I get this value inside a plugin ?

There is something like getHeaderVar("X-ThereisMy") ?