How often do I need to refresh my direct mail contact list?

[Mike Schorah]

I have a list from driving for dollars. I plan to send out direct mail every month. I got the list of the property owners from the county website.

How often do I need to refresh this list (due to property owners moving or transferring the title or selling the house, etc)?

How often do you refresh your list? This is a list of 1,000 properties.