I have the exact same problem. It started this weekend. My output for the zmlogprocess is also EXACTLY the same as the one posted. What happened?
The only thing i can gather might be this....
Code:
/etc/cron.daily/prelink:
/etc/cron.daily/prelink: line 47: 17559 Aborted /usr/sbin/prelink -av $PRELINK_OPTS >>/var/log/prelink.log 2>&1
After that the next Daily mail report showed only 15 mails, down from 123 the day before, but should have been around 300+ (spam testing). Every report since then has been "No Messages Found"
To add to this, the Server Status page would not update until I restarted Zimbra. Now it refreshes correctly.