Does any data get sent to matrix hq or element?
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What do you mean by “traditional video calling”? Are video calls not encrypted? Is traditional meaning out of the box video calling? What is the alternative?
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Since it’s not federated, joining or chatting with other servers won’t apply.
Disclaimer: I am not a synapse dev, but I have run a non-federated server for a long time.
Assuming you have fully disabled federation and Matrix.org provided services, data should not be leaving your instance. I run mine with bridges for services like Signal, IRC, and Discord, so as expected data goes out through the bridge software (via VPN).
To be extra safe, you could run it in a Docker container who’s network is limited to local, and an nginx proxy for Element.
If you interact with any other server on the network (meaning users on another server), all messages/attachments/metadata will be synced with all other servers by design.
Given the percentage of users on Matrix.org & servers they provide, some of your data will end up on Matrix HQ servers.
Their instance is not federated.
Somehow missed that part. But what would be the point of a defederated chat then?
I use mine like old school Trillion. Element is my Discord, Signal, IRC client. One thing open on my desktop to do them all.
Edit: For instance, Beeper (https://www.beeper.com/) is just a defederated Synapse server with bridges.
I want to set up XMPP gateways to do the same, but I would still feel comfortable federating since the network isn’t centralized around a single hub. The clients are a lot less weighty too.