[imp] pass client ip during authentication

[Systeembeheer BCS]

Using imp for authentication with dovecot IMAP, working fine. But now  
I would like to make use of dovecot's allow_nets feature to restrict  
logins from certain ip's. To make that work, imp should pass the  
client's ip (as seen by apache) to dovecot during authentication, but  
instead it passes 127.0.0.1 for both lip and rip. Any way to change  
this?

horde log:
2014-09-25T11:39:54+02:00 NOTICE: HORDE [horde] Login success for  
test at bezoekerscentrumsonsbeek.nl [192.168.4.101] to horde. [pid 6600  
on line 150 of "/var/www/horde/login.php"]

mail log:
Sep 25 11:39:54 BCS dovecot: imap-login: Login:  
user=<test at bezoekerscentrumsonsbeek.nl>, method=PLAIN, rip=127.0.0.1,  
lip=127.0.0.1, mpid=8382, TLS