It's still personal if you can guess it. For instance, you might be able to guess someone's GMail username by their Facebook vanity URL or their Hacker News use

It's still personal if you can guess it. For instance, you might be able to guess someone's GMail username by their Facebook vanity URL or their Hacker News username. That doesn't mean you can post their email all over the place. If it's not posted publicly by the person, it's private.