Recipients Cache under Additional Settings allows administrators to clear email recipients from the list that deems them invalid.
Email Security - Cloud keeps track of recipients that it has delivered emails to. This list is used to validate recipient addresses for incoming emails.
If message delivery to a specific recipient fails and there have been no previous successful deliveries within the past week, then the recipient is added to the recipients cache and marked invalid. After a recipient is marked invalid, future incoming emails to this recipient will be rejected. The "Manage Recipient Cache" feature allows admins to delete the addresses that the system has learned.
See Message analysis policies for dynamic or static recipient validation.
To remove email entries from the recipients cache:
Click in the Add entry to remove box.
Manually enter recipient addresses.
Click Submit.