This article describes how to access emails in case the main mail server is down.
In event of mail server outage, messages that can not be delivered to mailbox are stored on McAfee servers. To access those messages navigate to My Services > Email Protection > Manage Email Protection Settings > Email Continuity.
Another way to access the messages is to open the link from McAfee report:
For more information on the service, have a look at the article: McAfee Email Data Loss Protection and Email Continuity