The point is that those other apps don’t use email addresses as the handle to contact someone. If someone iMessages you, the iMessage might (appear to) come from their phone number, or it could (appear to) come from their email. If you have an iMessage contact that’s just an email and you iMessage them, it works fine. If you try to then add Android users to your group chat, everyone gets SMS and the iMessage user with an email handle gets an empty body email from AT&T with an attachment containing the SMS as a plaintext file. And then this user gets another empty email for every reply to that group text.

I'm fairly certain that "text to email" is a feature of MMS - I've used it a few times years before iPhones were around.

I don't remember if MMS is enabled by default in iOS but theres a toggle to disable it, and realistically there's very minimal real world use-case for MMS these days.

Yes, it’s an MMS feature. But iMessage makes it way too easy to “text to email” inadvertently when you start a group chat with some non-iPhone users. MMS sucks but it’s the universal way for iPhone and Android users to communicate without needing everyone to be on the same third-party messaging platform like WhatsApp. In my US-centric personal experience, there is no universally accepted messaging app you can be certain that everyone is on.

The universal option is SMS.

Oh, I have never come across that because I have avoided MMS like the plague ever since WhatsApp/Signal/any other cross platform messaging option with media capability became available.

On Apple's end, iMessage also supports email addresses as a user identifier (and it's the only one you get if you don't have an iPhone with an assigned phone number).

It's still not sending emails, though. The iPhone Messages app sends SMS, MMS, and iMessage; email is the responsibility of the Mail app.

They support email address for sms id as well. Pretty common for phishing.

The point is that iMessage lets you send to any contact and it’s not clear if it will send to their iMessage, which uses email as an identifier, or to their actual email inbox through mms.

It is clear in a non group conversation, since the contact will show up in a blue color in the “to” field.

In an MMS, it could be unclear, but only if you choose to put an email address in the “to” field. If you know it is an MMS, and you only use phone numbers, then it will not be an email.