[nikcub]

The obvious evolution of this would be to host email and allow users to forward:

  [e-mail] -> useremail

The fake non-routable emails can be a problem when you have to get in touch with contributors who are no longer active on Github.

Saw this problem in the bootstrap project where we still can't get in touch with ~10% of users to get them to approve the addition of an MIT license:

https://github.com/twbs/bootstrap/issues/2054

[simonw]

This would make it trivial to spam every user of GitHub though, by first spidering the site for public usernames.

[JohnTHaller]

Which would result in quite a lot of spam sent via GitHub's forwarder, which would then be marked as a spam server in Gmail and other providers, which would result in GitHub's server being blocked.