background refresh of dns cache

[mark david mcCreary]

I have a large mailing list that goes out at approximately the same time
each day.

A substaintial portion of the processing time is spent doing DNS lookups,
and I would like to reduce that time.

I am thinking that a background program that would continuously review the
existing DNS cache, and refresh each entry as the TTL gets close to
expiring it.

That is, when the next day's message comes in, the local DNS cache is
current for all domain names that were sent email the previous day.

Is there a program to accomplish this, or would this be considered a "bad"
idea.

Thank for any feedback.

mark