Vault admins have had the ability to put an entire user account on hold to preserve messages in that account. Over the next few days Google is releasing a feature that will give admins the ability to also have the option to target specific messages—for example, by date or with certain terms—for indefinite preservation in Vault.

For more information:
https://support.google.com/vault/answer/4359587
https://support.google.com/vault/answer/2473591