rlm_exec and authentication

Hello all, I wanna write an authentication script which will control the username&password pair from an IMAP server. Acutally the script is about ready but, i couldt find a way to execute from radius. I first tried rlm_perl which i thouhgt it will be better and easier But i had the error "undefined symbol: Perl_Tstack_sp_ptr (failed! run '/usr/sbin/freeradius -x' to find out why.)" Then i reinstalled freeradius checked the updates of perl etc but no solution.. And i decided to use rlm_exec for that. But i am not sure how will i use it as authentication. Anybody has an example regarding to that? Or even a solution for my rlm_perl Thank u Oguzhan Kayhan