How to make my iMac a server and find my server address

Have you tried setting up your home Mac as a VPN server? I use a free app called VPN Enabler. It's free for El Capitan, Sierra and High Sierra. The link I provided should give you the information you need to setup the app. You will need a registered domain name that you can get free from NOIP.com for personal use.

You could also use the free app (free for personal use) TeamViewer to screen share with your home server. It also allows file transfers.

I can VPN from any Mac or iPhone on the internet to my home server. Or I can use TeamViewer from any of those devices to get to my home server. It just depends what I'm trying to do.

192.168.*.* are non-routing IP addresses used by home routers for devices inside the home. The Router has an external Internet facing address that can be addressed from the outside world.

While at home, if you Google "what is my ip", it will tell you your Router's Internet facing IP address.

It is also possible to get a dynamic DNS name from a service such as No-IP.com or DynDNS.com. Then you run a utility on your iMac that keeps the dynamic DNS name up-to-date. Then you can use a name to find your home router.

If your Transfer software talks to your router and sets up a way to connect, then this might work.

If your Transfer app does not do this, then you would need to set up some Port Forwarding in your router. This is a non-trivial task.

keg55 has a good suggestion of setting up a VPN server on your iMac and connecting that way.

Oh Yea. Does work have a corporate Firewall? If it does, that could block your ability to make random connections to systems outside your office.

Use a hosting or a dropbox-like service, push the files to that, and then fetch the files from the local network.

Opening up ports through your firewall—which is where you’re headed here—opens those same ports for zillions of random folks and botnets to poke at the servers on the target network, and the interested folks will find and will poke and all poking usually starting within minutes. Any weaknesses of the setup or the security or the passwords are then tested. Endlessly.

If you really want to set this up, you’ll need a dynamic DNS translation for your external dynamic IP address (dynamic DNS means you don’t have to track your external IP address as that changes) (some mid-grade firewalls can be configured for dynamic DNS; the firewall will update your entry in the dynamic DNS provider when your ISP changes your external IP address), and you’ll need to set up what’s usually called port forwarding on your firewall, as that maps your external IP address and port through NAT and into your internal IP address and port), and you’ll want that port forwarding to reference the static IP address of the target computer on your internal network. Set up that target computer either using a static assignment in your DHCP server, or just manually set it. Use sftp here on TCP port 22 (ssh and sftp), or upgrade this whole environment and use a firewall with an embedded VPN server.

You’ll learn a fair amount about IP and routing and DNS and dynamic DNS and VPNs here, too.

If you go for the VPN solution—you’ll learn a lot about networking here—I’d use a firewall-based VPN server and not a host-based VPN server. This avoids passing the VPN through NAT. Which is workable, but that’s more complex and there can be some oddities if it’s not all set up correctly. I’d usually prefer to have a mid-grade firewall with an embedded VPN server.

Another approach is a Synology box or other network storage box, as those can be exposed to the ‘net.

If you open up local access into your network, you’ll need to keep all of that current and patched, too. In addition to secure passwords and related.

Or push the files somewhere, and then switch networks and pull the files. Dropbox, and any number of other storage hosting providers are available for that.

In no particular order...

iCloud, Dropbox, and other services are commonly used for this sort of thing, and for synchronizing the files across various systems. Keepijg the most recent copy, and distributing it across the various devices and hosts sharing the service.

Or running your own server and storage configuration on a hosting service.

You’re headed for manually managing a whole lot with the current approach, not the least of which is the security and network access.

Somewhat more involved setups might use OwnCloud or NextCloud servers, or FreeNAS or Synology network attached storage.

Network firewalls are designed to prevent what you want from working, as it’s indistinguishable from the usual sorts of network shenanigans.

And there might be a market for VPN services, though services such as LogMeIn are commonly used for that.