Question --- I haven't done much webdev stuff so this may sound silly, but --- why can't PMs work that way? Like, why can't I send markbao a private message by sending an email to [email protected]? And then the site could forward it on to his email address, or if the site wants to get fancy they'd store it in a database and display them as "comments" in the target user's "editing profile" screen (whenever you edit your own profile).

More than that though, I'd like to learn about the nitty-gritty of e-mail. As a game developer I do mostly C++ application code, so everyone else probably has way more knowledge than I... But for example I'd like to be able to embed the ability for my programs to send emails (as a debugging mechanism). Or even receive emails! (Imagine taking down some number of your servers, for patching purposes, by sending a "console command" as an email to [email protected]. Or running queries on your servers by sending the query as an email, and then they email back the response.

How would I write a C++ function like:

  bool SendEmail( const tchar* destination_email_address, const tchar* subject, const tchar* body );

When I've needed to send mail from C, I just call a CLI mail user agent like http://en.wikipedia.org/wiki/Mailx, and configure it to talk to a local MTA (traditionally sendmail), which buffers messages locally before sending them to a real mail server on the internet (I use authsmtp). Python has a nice builtin library for talking to my local SMTP server like, I suspect, many other modern languages.

There's no technical reason why email addresses like [email protected] can't work. In fact, I'd argue Tumblr/Posterous have some of the same core ideas you're proposing.

A primary reason why a site wouldn't support PMs to [email protected] is that there is no access control. The address would get spammed too easily from senders with no affiliation with Hacker News. The current mechanism of only supporting messaging within the site limits this.

Sometimes it's interesting to think about how much better the world could be if we could design things without worrying about griefers.