Are they going to arrest Zuckerberg and Tim Cook next for the encryption in WhatsApp and iMessage?
We don’t trust proprietary stuff because we’ve been burned by it, if there’s an open standard, even a worse one: use it.
If it’s really that bad, we need to improve the standard.
You connect from any compatible client; and the effort that has gone in to the Mail client for iOS means it’s a decent enough mail client for non-iCloud mail accounts too.
Apples closed ecosystem is mostly its developer tooling and iMessage.
If your rationale against first-party backdoors relies on this logic, then you're in for a really big surprise when you read the Snowden leaks.
I wouldn't. I don't trust Apple hardware or software, and I don't see why anyone who cares about these issues ever would. But fortunately Telegram runs on devices and OSes from a wide range of suppliers, many of which might be less open to the influences that apply to Apple.