As of January 1, 2018, the U.S. Copyright Office will implement new regulations that will impact online service providers – even those that have already registered an agent.
Under Digital Millennium Copyright Act (DMCA) safe harbor provisions, online service providers must designate an agent with the Copyright Office to receive notifications of claimed infringements. The DMCA protects service providers from liability for copyright infringement arising from content posted by others on the provider’s websites. Even those who have previously designated an agent via the Copyright Office’s paper submission process must re-register with the electronic system by December 31, 2017. Link: https://dmca.copyright.gov/osp/login.html
Additionally, agent designations are no longer in perpetuity, and must be re-registered every three years.