We've used Sendbloom for this, they have an automated response system with the ability to bump previous conversations and a programmatic funnel that solves these same problems.
Thanks for the shout-out :) (am part of the Sendbloom team).
I wish the PersistIQ team well, it's really exciting to see other entrants in this space, especially one that's backed by YC. Verifies that there is a demand, or at least a projected demand for this sort of an application.