How Do I Keep A Master Mailing List?

[Burt L.]

I have done multiple mailing lists and am seeing some names appear on lists that I have bought before. I use the sort feature at Listsource to avoid this, but some come through anyway. Their sort feature - I'm not using the right term - only goes back six months though, as they delete your list(s) after the six month period.

Do you keep a master list beyond what the lead provider offers - to prevent mailing to people you have already touched and have asked to be removed, or were undeliverables?