[Dovecot] Dovecot Proxy and environment variables

[BaQs]

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 !