Open the Retentions page (Email Archive => Settings => Retentions) and configure the duration of storing the archived item to 10 years. Click on + new and the “Retention repository” window opens. Name your retention (“10 years”) and specify the retention time in months (120).
Note: During this retention time, the archived items will not be deleted from the selected storage. The first created retention will be automatically set to default. This option is configurable on the Retentions page, using the given retention’s context menu. Default retentions are used by the Mail app and OWA integration (by archiving/restoring from the mailbox directly). For more information, refer to the online guide here.