The Revoke Emails List field contains the email IDs of the users whose access is revoked. You must click the Permission to View action on the Event detail view. The list of recipients is displayed. You must select the check box for the recipients to whom you wish to restore the access. Once the access is restored the Unrevoke Emails List field displays the email IDs of the users to whom you restored the access.
When the expiration time is different in the Nightfall policy and the email sent, Nightfall picks the shortest time period. In this case, the end-user has set a time-period of 1 hour in the Email (which is a shorter time period than 2 hours). Hence the email expires after 1 hour.
The Nightfall admin has revoked access to the recipient from the Nightfall encryption event. Contact your Nightfall admin to restore the access.
Your Nightfall admin has configured Encryption settings in an encryption policy. So, even if you have not configured any encryption settings, the policy automatically implements the encryption settings enforced by your Nightfall admin.
You can restore access to a sent email which is expired. Just go to your sent emails list. Open the required email, and set a new expiry date for the email. The recipients can now access the email until the new expiry date is reached. You can also disable expiration totally. In the case, this recipients can view the Email forever, until you enable expiration again.