A mere written demand to preserve ESI does not create a binding legal duty on a third party to not destroy the data. In its Commentary on Rule 45 Subpoenas to Non-Parties, the Sedona Conference recommends of the use of preservation subpoena.
It cites Koncelik v. Savient Pharms., Inc., No. 08 Civ. 10262, 2009 WL 2448029, at *2 (S.D.N.Y. Aug. 10, 2009) (“The only thing that is certain is that without preservation subpoenas, the third party corporations in possession of potentially relevant information are free to destroy that information.”). Courts may issue preservation subpoenas when a stay has postponed discovery, or in time consuming multidistrict coordinated cases. These subpoenas must be narrowly tailored to avoid undue burden.