It also is used to separate the username from the domain. We don't want to allow special characters in the address.
Domain is symbolic name.
Check if it's valid. Of course not. But that's essentially what you do when you allow politicians to set the rules by which they are elected. RealCampaignReform.org was founded in the belief that the most important election rules we have are in the United States Constitution. You should have the freedom to speak your mind, to support or oppose any candidate you choose, and to join together with others for the same purpose.