That's a lot of assumption, there. You assume we all have an extra box lying around to serve. You assume we all have the DIY attitude--or the time--to set one up. You assume that all E-mail users are smart enough to do this. And you assume (for my case, at least) that setting up AND maintaining a premise e-mail server is something we all WANT to do (after, you know, a long day of tending to company servers and equipment). And, finally, there's the assumption that the irrelevance of this avenue (as it IS outside the scope of the OP's question) is warranted or welcomed feedback.