Some Windows Live Messenger users create their user ID via the Microsoft Passport service, which enables them to sign up to use any email address for their ID. When they sign up, they get an email at that email address, which they need to open to verify their access to that email account. If the user does not go through this email verification process, the user's ID is displayed with '(E-mail Address Not Verified).'

Exercise caution if you get an Add invite or some other communication from a Windows Live user whose ID ends with ‘(E-mail Address not Verified)'. You may want to confirm this person’s identity before proceeding with your correspondence.