This document describes the error message "DNS Cache Init Failure."
What should I do when I see the error message, "DNS Cache Init Failure?"
This is a boot up error reported by the Cisco Email Security Appliance (ESA). It occurs when the DNS cache fails to initialize at boot time. It can also occur if a dnsflush is performed and the cache cannot reinitialize.
This failure is not fatal, and the cache will re-initialize at a defined interval. If you see this error message only once or twice, the DNS cache must have initialized successfully during one of the subsequent intervals. If the appliance continually fails to initialize the DNS cache, it will be unable to resolve hostnames and IP address, and all email messages will be undeliverable.
Unless you see this alert more then once per reboot you can safely ignore it.