I have one server in intranet (joined to domain, accessible via domain account) and the other one in extranet (not joined to domain, accessible via hopping station using a local account). Shared folders on intranet servers are accessible for domain users, who may update the content as necessary. These folders need to be synchronized (1 way synchronization) to extranet servers. Extranet servers (or severs in DMZ) are protected from any basic access and access to specific ports are allowed only to specific devices (RDP, port 3389, is allowed only to certain subnet; HTTP, port 80, is allowed only to HW Load Balancers; etc.). Due to this, I can't use File Sharing which makes robocopy out of game and I can't use DFS-R as both servers are not in a domain.
I've searched for some free synchronization applications but all of them are based on synchronization between two servers that can access each other. I'm looking for server-client synchronization software, that works on specific port (this will be excluded in Firewall). My idea is, that client (server in intranet) will inform the server (server in extranet), that some files were added/modified/deleted and will send these files/changes to server to store them in configured folder. Of course, ACL is not important here - all files stored on the destination server will have default (inherited) rights from the parent folder.
In the past, I've used a very old tool from Microsoft called "Microsoft Site Server 3.0 Content Deployment". This tool is older than 10 years and does not work any more - it requires a domain user account which could not be found if DFL and FFL are too high (>W2K12).
Thanks for your help or suggestions.