IIRC ESR inherited an earlier POP client, hacked the "deliver to local SMTP port" onto it and tarted up the user interface.

I've still never found a major piece of systems work ESR has done that's found a wide user base. Fetchmail is something you could hack up in a weekend, not a serious piece of software engineering. He talks a good system... if you happen to think the 'bazaar' approach is anything other than contemptible ;P