Registrant contact information is maintained by the registrar. The failure of a Registered Name Holder[1] to furnish up-to-date contact information with its Registrar[2] may result in the forfeiture of rights[3] up to and including the suspension or cancellation of the registration itself.[4]

Point being that, short of transfer Auth-Codes[5], a verification link sent to the registrant's email address by the DNS provider is the functional equivalent of nearly the most that a registrar may be required to do in order to contact and/or verify a registrant.

[1] https://www.icann.org/resources/pages/ra-agreement-2009-05-2...

[2] https://www.icann.org/resources/pages/ra-agreement-2009-05-2...

[3] https://www.icann.org/resources/pages/benefits-2013-09-16-en

[4] https://www.icann.org/resources/pages/registration-data-accu...

[5] https://www.icann.org/resources/pages/auth-2013-05-03-en