When will the retained email be purged from the eDiscovery storage?

When will the retained email be purged from the eDiscovery storage?

Mails are retained according to the Default retention policy or the Custom retention policy defined by the administrator. Mails older than the set retention period are considered as expired emails and are purged from storage once every 10 days.

Emails on hold will not be deleted until the hold is removed by the administrator.