I cannot achieve that Posgrey works with Zimbra Open Source. The information is the following:
Debian 2.6.24-etchnhalf.1-686
Release 5.0.18_GA_3011.DEBIAN4.0 DEBIAN4.0 FOSS edition
I install Postgrey (apt-get install postgrey).
Add the restrictions file (jed /opt/zimbra/conf/postfix_recipient_restrictions.cf) with line %%contains VAR:zimbraMtaRestriction check_policy_service inet:
Add to the domain the line:
zmprov mcf +zimbraMtaRestriction "check_policy_service inet:"
Add Postgrey configuration:
POSTGREY_OPTS="--inet= --delay=300 --max-age=35
Restart Postgrey and Postfix:
su - zimbra -c"postfix reload"
su - zimbra -c"zmcontrol stop"
su - zimbra -c"zmcontrol start"

But the greylisting donīt works:

Oct 20 13:18:57 pepe postfix/smtp[9266]: 913094E0203: to=<pablo@pepe.com>, relay=[]:10024, delay=6.7, delays=0.88/0.01/0.01/5.8, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as D94E74E08A1)
Oct 20 13:18:57 pepe postfix/qmgr[8677]: 913094E0203: removed
Oct 20 13:18:57 pepe postfix/lmtp[9323]: D94E74E08A1: to=<pablo@pepe.com>, relay=pepe.com [192.168.x.x]:7025, delay=0.77, delays=0.02/0.02/0.05/0.69, dsn=2.1.5, status=sent (250 2.1.5 OK)

Forgive for my English. I am grateful for any help. Regards,