I'm sure others allowed posting by email before. BrightKite was a fantastic social network that was location-based, and you could post via email. My friends and I still miss it... https://en.m.wikipedia.org/wiki/Brightkite

I tried something along those lines a few years ago… https://publicemails.com

I absolutely loved Posterous, major shame it was squashed after being bought(?).

MSN Spaces had this feature back in 2006! Makes me feel nostalgic!

Oh man, the nostalgia I just had. I used a Peek to post to Posterous.