Retention Policy (Retention Schedule)

WORM (Write Once, Read Many) storage allows data to be written a single time and then read repeatedly but never altered or deleted before its retention period expires. WORM is a core requirement of regulations such as SEC Rule 17a-4 because it makes archived records tamper-evident and immutable.

Immutability is the property that a stored record cannot be modified or overwritten once committed. Immutable archives use techniques such as WORM storage, cryptographic hashing, and write-protection to guarantee that preserved data is identical to what was originally captured.

Defensible deletion is the documented, policy-driven disposal of data that has met its retention requirement and is not subject to any legal hold. Done correctly — with consistent policies and audit trails — it reduces storage cost, risk, and discovery scope while standing up to legal scrutiny.

Single-instance storage, or deduplication, stores only one copy of identical content (such as a message sent to many recipients or a repeated attachment) while preserving each reference. It reduces archive size and cost without losing any record.