[NoGravitas]

I worked at a web hosting company 1999-2005 that used qmail, and while there were many things wrong with qmail, due to it not being designed for the realities of email circa 2001, backscatter was by far the worst. We were processing significantly more backscatter than valid email, and to the best of my knowledge, the patches to address it didn't yet exist.

We certainly should have switched mail servers, but qmail was deeply ingrained in our home-grown hosting automation system, and it would have been a big deal to change.