File Synchronisation between two NAS Units

Description of support work: I need a file Synchronisation utility to automatically synchronise files from a Local NAS Unit to a Remote NAS Unit over the Internet.The utility can be one based on an existing program such a s WinScp or a specific utility already available which meets the requirements below.

The local NAS Unit has an IP Address of 192.168.0.101 and the source folder will be \192.168.0.101\public

The Offsite Nas Unit is a has a DDNS address of remote.dnsalias.net. Its local IP address is 192.168.5.101 and the destination folder is \\192.168.5.101\public

Currently I am copying the files manually by ftp to the remote NAS Unit but I want it automated whenever a file changes on the Local NAS Unit

Notes
1. The synchronisation will always be one way only i.e. from the local to the remote
2. Verification of files must be included.
3 The ability to specify a start and end windows is necessary e.g. start at 20:00 hours and continue until 08:00 hours the next day or until all the files have been synchronised.
4 In the event of a network disconnection or interruption the synchronisation process should be able to continue from when the interruption occurred without having to restart from the beginning.
5 The ability to send and email when the synchronisation have completed.
Extra notes: