To ensure that the system clock on a host machine is as accurate as possible, many organizations host a Network Time Protocol (NTP) server within their network. A ZixGateway appliance host machine is able to use an NTP time source if it is available in your network. NTP requires ports 123 and/or 536 through firewalls.
If you have an NTP server, type the IP address of the NTP host in the Network Time Protocol Server field. Only one NTP host IP address can be entered in this field.
If you do not have an NTP server, you may be able to use a publicly available NTP server, or leave this parameter empty.