The following text is directly from: https://www.copyright.gov/dmca-directory/
A relevant F.A.Q. can be found at https://www.copyright.gov/dmca-directory/faq.html
Service Provider Designation of Agent to Receive Notifications of Claimed Infringement
The Digital Millennium Copyright Act (“DMCA”) provides safe harbors from copyright infringement liability for online service providers. In order to qualify for safe harbor protection, certain kinds of service providers—for example, those that allow users to post or store material on their systems, and search engines, directories, and other information location tools— must designate an agent to receive notifications of claimed copyright infringement. To designate an agent, a service provider must do two things: (1) make certain contact information for the agent available to the public on its website; and (2) provide the same information to the Copyright Office, which maintains a centralized online directory of designated agent contact information for public use. The service provider must also ensure that this information is up to date.
In December 2016, the Office introduced an online registration system and electronically generated directory to replace the Office’s old paper-based system and directory. Accordingly, the Office no longer accepts paper designations. To designate an agent, a service provider must register with and use the Office’s online system.
Transition period: Any service provider that has designated an agent with the Office prior to December 1, 2016, in order to maintain an active designation with the Office, must submit a new designation electronically using the online registration system by December 31, 2017. Any designation not made through the online registration system will expire and become invalid after December 31, 2017. Until then, the Copyright Office will maintain two directories of designated agents: the directory consisting of paper designations made pursuant to the Office’s prior interim regulations which were in effect between November 3, 1998 and November 30, 2016 (the “old directory”), and the directory consisting of designations made electronically through the online registration system (the “new directory”). During the transition period, a compliant designation in either the old directory or the new directory will satisfy the service provider’s obligation under section 512(c)(2) to designate an agent with the Copyright Office. During the transition period, to search for a service provider’s most up-to-date designation, begin by using the new directory. The old directory should only be consulted if a service provider has not yet designated an agent in the new directory.