LinkedIn is a networking site for employees and employers. To register, only one email can be used for that purpose. If one tries to register and they already have an account with that email, they will receive a message stating so. Though LinkedIn only allows one email to register, one can have multiple emails under their account to manage.
LinkedIn recommends each user to have a primary email and additional emails on their accounts. This is useful; for instance, if someone gets locked out of their primary email, they can use their additional email to log in and view the account.