[Dovecot] Dovecot Proxy and environment variables

Dear list,

First of all, I am French so excuse my bad english.

I am currently using dovecot proxy feature, using sql backend.

I "proxy" the imap/pop requests to another server, let's say server2.

On server2, I use a script to keep up to date a "pop before smtp auth" database.

I used mail_executable = /path/to/this/script.sh ...

My problem is: the $IP environment variable on server2 is the proxy's IP.

How could I give a variable from proxy to server2, or simply get the real client public IP ?

Thanks a lot in advance for your answers

Pierre.

PS: let me also thank very much dovecot developers and community !