In Google Cloud Storage, you can set a retention period that applies to all of the data (Mail/Drive/Chat).
In CloudM Archive, you can set different retention periods for Mail, Drive and Chat.
If the retention period is set in Google, the data will be purged in Google Cloud Storage, not via CloudM. This will affect how we index the data so you could still see deleted data appearing in CloudM.
It is strongly advised to only set the retention policies in CloudM to stop any conflicts.