Telegram is one of the few messengers that actually enables you to use any Telegram client available, or write your own[1].

The protocol that is de facto Telegram is called MProto[2], and is publicly available.

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[1]: https://telegram.org/apps

[2]: https://core.telegram.org/mtproto

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edit: The main difference between email and Telegram, is that anyone can host email servers, while Telegram manages theirs.

edit2: MProto being widely available to study, one could perhaps reverse-engineer their own server - but that hasn't been a desire to accomplish this from what I can see. Much of the value-proposal of Telegram is their Service as a whole.

Telegram is centralised and siloed, where email isn't. You just can't compare the two.

> You just can't compare the two.

You just did.

I was responding to the claim that Telegram wasn't providing a protocol or ability for developers to author their own clients.

And point taken—I didn’t know about this, so Telegram was not an ideal example. But, as you point out, it still is not quite a decentralized as email, and, as a protocol, does not have email’s universal character. But thanks for the interesting information.