For me, it wouldn't so much the annoyance of getting mail but the annoyance of having my work follow me around, along the lines of "It's none of their business what I do for a living".
When I leave the office at 6pm, my work should have no more relevance until the following morning. Same when I quit a company. I might choose to tell people where I work/worked, but it should be a choice, and I should be able to choose how much I tell people about my work. Having mailing list posts and maybe even cvs commits might be too detailed. Maybe waaay too detailed.
In my current an previous job I've chosen to disclose lots about what I do, but that's because it's also my hobby. I "live" my job, to an extent. I wouldn't expect co-workers to automatically also publicise this much about their nine-to-five life.
I agree that public discussion *shouldn't* be seen as an endorsement or an announcement or an official communication, but it often is. Fixing that from the recipient's end requires changing modern culture / human nature - a big ask :-) Fixing from the sender's end will be easier IMO, and maybe pseudonyms would mostly fix it.