They're variants of the same software stack. But that's sort of the thing: email filtering (the only thing that makes email useful) requires tuning and heuris

They're variants of the same software stack. But that's sort of the thing: email filtering (the only thing that makes email useful) requires tuning and heuristics. Decisions that are effective for personal email may not be for the spam faced by corporate clients, and vice versa. No one (at least no one serious) thinks you can just implement some RFCs and get a product that works and doesn't suck. Life just isn't like that.