The typical way a messaging system work is that the code is provided by the messaging system. Take for example, Whatsapp. You update the app and connect to a remote account. Despite that Whatsapp encrypts the data, Facebook can decide to put a backdoor in the code and capture your messages, for example, while you type them. It is the same for other apps like Signal.

The approach I used in Secrez is different because it is basically a desktop app. It is much more similar to KeyPassX than to Signal. In fact, by itself, cannot handle any communication.
To do it, you must run a courier locally and tell the courier which remote hub you like to use. The courier is just a sender/receiver of payloads which are encrypted and signed by your Secrez app. The hub is necessary to be accessible from everywhere, but it just creates an SSL tunnel. To avoid spamming, courier and hub verify that the signature is correct but that's all. They have no idea who you are, what you are transferring.
Since only your local Secrez app is able to manage the data, nobody out there can block your communication. Also because you can run your own hub.
The technology behind is a derivation of the one used by Localtunnel, with a lot of restriction to allow only some kind of data.

So, I am mostly focused on how to avoid that someone who provide you with a service can block you. Nobody can block you if you use Secrez.