Junk mail sorter

The recent flap about The Sun posting their crap to all and sundry made me realise the solution to everyone's problems:

The postman must deliver all post to its destination and can't choose not to, even if signs are up saying 'No junk mail' or 'The Sun is not welcome here', so what is required is a second letterbox in everyone's doors for junk mail only.

Behind the junk letterbox would be a small frame holding a bin bag open to save the faff and temper of the householder. Of course this would mean more work for the postman, but once these letter boxes are in wide use, junk mail will start to be bundled together rather than being mixed with the real desirable post, thus actually saving time at the sorting office.

This seems like something that would already be half or fully baked, but I couldn't find it already, so appoligies if my searching has been insufficient.