We have programmed a very usefull utility for verifying large lists of email records. The project is currently a work in progress, and a way to integrating a multi-threaded approach is being worked on. Once all the bugs and kinks are out of it, we'll release version 2.0.
The software is a .NET Application, and you might need the .NET 1.1 Framework library. If you don't already have this framework, which is used in many new applications, please use the following link to download it for free:
Remember that this program is a work in progress, meaning that the threading doesn't work just yet, and it runs/verifies pretty slow right now without them, but very soon it will be able to run as many as 500-1000 threads... those with dedicated Win2K3 boxes, get ready!