You have updated the Host Name and IP Address Mapping in order to directly map a hostname to an IP, bypassing DNS. However, after saving the configuration the direct mapping does not work.
Release : 10.8.0
In version 10.8.0 of the Messaging Gateway, the Host Name and IP Address Mapping configuration saves, but the process needed to update the operating system itself is not completed upon saving the configuration.
This issue has been addressed in Messaging Gateway version 10.8.1.
As a workaround for 10.8.0, the mapping can be completed by manually restarting the osconfig service or rebooting the appliance.