Every platform uses a kind of identifier per user. This identifier is unique and specific for each user, and is used in the platform operation to link the user to all of his actions, communities, pictures, messages,... At ThreeAndMore we have chosen to use the e-mailaddress as and identifier. This creates extra security as a verfication code can be sent to the user, and creates an easy way to communicate. Once you've registered to the platform, this e-mailaddress will always be used to log in, and for all further communication. You can add/show other e-mailaddresses within your different community contexts, but the primary e-mailaddress will always remain the same.