Port seems to be open, but connection refused

If your server is listening on the localhost interface only, you won't be able to access it from a remote computer. This appears to be your primary problem, as only 127.0.0.1:3000 is listed in your netstat output.

You will also need to ensure that "mydomain.com" resolves to the correct IP address for your machine, such that connecting to it will result in communication with the external interface of that machine.

I had this problem recently with a nodejs HTTPS server, and the solution to it was not to use "localhost", "127.0.0.1" or even the domain name. It was to use "0.0.0.0"

I believe this acts as a wildcard, now allowing for public resolution via the domain name and it also works with "localhost"

Edit: Here's a link to a serverfault page on the 0.0.0.0 topic: https://serverfault.com/questions/78048/whats-the-difference-between-ip-address-0-0-0-0-and-127-0-0-1

Is there any chance that you are using AWS or any other cloud services? In that case port should be opened on cloud service level. In particular among AWS you should be looking for "Security Groups" where you need to open access to port 3000.