ML mail writes:

I am not running a local DNS cache on the server. As suggested using a local DNS cache would simply fix this issue but I am more interested to know what is generating these slow DNS queries...

As another poster has commented, a slow DNS response may not be anything related to your setup, but caused by upstream DNS service. Slow DNS response or timeouts is not uncommon, and if you're only getting 6 per day, you should count yourself lucky.

If it's the same FDQN that's being delayed, you can maybe run an online DNS diagnostic -- they're may be some bum delegation or unsync'd data you can report, but it will probably not be worth your time to chase this to ground unless it's causing your client to get hung.

Joseph Tam <jtam.home@gmail.com>