O script abaixo pode ser colocar em /usr/local/sbin/cria-abook-global

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#!/bin/bash
LISTA="/chroot/emexis-webmail/emexis-webmail-userconf/data/global.abook"
DOM=`domainname -d`
rm -f $LISTA

for I in `cat /etc/passwd | grep 1000 | cut -d: -f1,5 | sed s/" "/"+"/g`
do
        USR=`echo "$I" | cut -d: -f1 | sed s/"+"/" "/g`
        NOME=`echo "$I" | cut -d: -f2 | sed s/"+"/" "/g`
        echo "$USR|$NOME||$USR@$DOM|" >> $LISTA
done

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Depois é só criar um agendamento para atualizar a lista global de todos os usuários

# vim /etc/crontab

Adiciona:

00 00 * * * root /usr/local/sbin/cria-abook-global