[PERDITION-USERS] how to check pop3 user and password from /etc/shadow only...

Dear all, I've already setup perdition as my one redhat sendmail server that harddisk is almost full, so i want to use perdition to migrate some users to another redhat sendmail server... but..how to do that check pop3 user and password from /etc/shadow only.. my existing sendmail server is very simple configuration...so i didn't have any database to store username and passwords also, i want to divide half of pool of users(for example, total users=20) to old server A and another 10 users to server B... then i have 2 lists of user...i got a headache about my openwebmail....how to automatically move list-A-users to server A and list-B-users to server B when they want to login to openwebmail... sorry for this stupid question...i'm newbabie on setup linux server... thx again.. regards, winnie