[Dovecot] login_trusted_networks from webmail ?

I'd like to get the IP-address of the webmail-klient logged in my maillog (for being compliant with coming data retention policies). I've noticed that with login_trusted_networks pointing at my dovecot directors, we get rip=client-ip logged on the backends. How is the proxy providing this to the dovecot backends? Anybody know what magic we need to implement in our webmail-solution to be able to forward the webmail-client-ip and have it logged as rip= in dovecot?

I belive it will be enough to have it logged as rip= on the directors, maybe not needed to be forwarded all the way to the backends (but that would be nice as well).

-jf