When a dispute is coming, the first duty is to preserve. This writes the notice that says so, keeps the register of who was sent it and when they acknowledged it, chases the ones who have not answered, and writes the release when the duty ends. The question asked later is never "did you mean to preserve"; it is "who did you tell, and when", and that has to be a document.
Anyone who holds material that may matter, including the people who administer the systems.
The notice says what to stop, not only what to keep. Most material is lost to a routine that nobody thought about: a retention rule, an auto-archive, a device trade-in, somebody tidying up. The notice names those, because "preserve everything relevant" does not stop any of them.
The register is the point. Who was sent it, when, when they acknowledged, and what they said they hold. Anyone sent a notice a week ago without answering is marked, and the reminder that chases them quotes the original notice.
Release is part of the process. A hold that is never lifted quietly becomes a hold nobody follows. The release notice says the duty has ended, that ordinary retention applies from today rather than retrospectively, and that another hold on the same material is unaffected.
It does not decide whether a duty exists. When a duty to preserve arises, how wide it goes and what your jurisdiction expects are legal questions. This writes the notice and keeps the record; the judgement is yours.
Nothing leaves this tab. The hold and the register are kept in this browser and, with a folder connected, in it. The notices are text you paste into your own email.
Generally when litigation is reasonably anticipated, which is often well before anything is filed: a letter before action, a serious complaint, a regulator's enquiry. Erring early costs little; erring late is what gets called spoliation.
Anyone who holds relevant material, which is wider than the people involved in the dispute: assistants, former team members, whoever administers the mailbox or the shared drive, and often IT, who can stop the automatic deletion that no individual controls.
No, but the register is per person, and "one per custodian" writes each notice addressed by name in a single file so you can paste each one into its own email. That is what makes the acknowledgement meaningful.
Say so at once and record it. The notice tells custodians the same thing. Deletion before a hold is usually a routine event that can be explained; concealing it afterwards is not.