Quick tooltip for Zimbra, for exporting all user’s contacts in one shot:

for i in $(zmaccts | grep -v never | grep @yourdomain.com | awk '{print $1}') ; do zmmailbox -z -m $i getRestURL '/Contacts' > /tmp/contacts_$i.csv ; done

This will export only main contacts folder, and of course it must be run as zimbra user.