I've got Zimbra 8.0.0 NE running on Ubuntu 12.04.1 LTS. Over the past week or so we've seen some large spikes in traffic coming from the network that it's sitting on, and while investigating the issue I noticed that the Zimbra server is sending out ridiculous amounts of DNS queries. In the vicinity of 10-30 per second, every few seconds.
We don't have that much traffic coming through that server, so I can't imagine why it would be doing so many lookups.
It's setup with split DNS as per the Zimbra guidelines. We've got another Zimbra 8.0.0 FOSS running on Ubuntu 12.04.1 LTS on the same network, setup exactly the same way, but it's not having the same issue with these DNS lookups.
Anyone have any light to shed on this? Let me know if you need any diagnostic information from the server and I'll post it up.