All I can share is that I only have helped people uninstall it. People get rather touchy that it works on some machines but not others. I can't explain it either.
Whenever I try to start IncrediMail, I see their logo and hear the "WELCOME" message. The window opens and within a few seconds my system freezes. The screen message reads: "The program has performed an illegal operation and will be shut down. If the problem persists, contact the program vendor." My only option at this point is to push the reset button on my computer and reboot. IncrediMail tech support has not responded to my request for assistance.