An information processing system comprising: a user terminal used by a user; an information processing apparatus configured to authenticate the user; an external authentication apparatus configured to authenticate the user separately from the information processing apparatus; a service providing server configured to provide a service to the user authenticated by information processing apparatus; and a verification device, wherein the information processing apparatus comprises: a storage storing restriction information indicating a restriction that a first mail address of the user registered in the external authentication apparatus is to satisfy in order to be permitted to use the information processing apparatus based on an authentication linkage with the external authentication apparatus, the first mail address being not notified from the external authentication apparatus to the authentication server; and a processor configured to: acquire first information indicating authentication success, the first information being issued by the external authentication apparatus and including a second mail address generated by the external authentication apparatus in association with the first mail address, transmit, to the second mail address included in the first information, second information requesting execution of communication with the verification device, acquire, from the verification device, a verification result as to whether the first mail address satisfies the restriction, the first mail address being a transmission source of the communication executed in response to the second information, and, in a case where the verification result indicates that the first mail address does not satisfy the restriction, perform control not to permit an authentication linkage with the external authentication apparatus for the user. a user terminal used by a user; an information processing apparatus configured to authenticate the user; an external authentication apparatus configured to authenticate the user separately from the information processing apparatus; a service providing server configured to provide a service to the user authenticated by information processing apparatus; and a verification device, a storage storing restriction information indicating a restriction that a first mail address of the user registered in the external authentication apparatus is to satisfy in order to be permitted to use the information processing apparatus based on an authentication linkage with the external authentication apparatus, the first mail address being not notified from the external authentication apparatus to the authentication server; and a processor configured to: acquire first information indicating authentication success, the first information being issued by the external authentication apparatus and including a second mail address generated by the external authentication apparatus in association with the first mail address, transmit, to the second mail address included in the first information, second information requesting execution of communication with the verification device, acquire, from the verification device, a verification result as to whether the first mail address satisfies the restriction, the first mail address being a transmission source of the communication executed in response to the second information, and, in a case where the verification result indicates that the first mail address does not satisfy the restriction, perform control not to permit an authentication linkage with the external authentication apparatus for the user. acquire first information indicating authentication success, the first information being issued by the external authentication apparatus and including a second mail address generated by the external authentication apparatus in association with the first mail address, transmit, to the second mail address included in the first information, second information requesting execution of communication with the verification device, acquire, from the verification device, a verification result as to whether the first mail address satisfies the restriction, the first mail address being a transmission source of the communication executed in response to the second information, and, in a case where the verification result indicates that the first mail address does not satisfy the restriction, perform control not to permit an authentication linkage with the external authentication apparatus for the user.