I am new to the Fediverse. I vaguely understand how Lemmy instances broadcast content to each other, but I was surprised to find Lemmy communities on kbin. How does that work?

https://feddit.uk/post/101886

I am new to the Fediverse. I vaguely understand how Lemmy instances broadcast content to each other, but I was surprised to find Lemmy communities on kbin. How does that work? - Feddit UK

And it also seems that mastodon can also be “syndicated” to these other communities, and vice versa? Is that true? Are there limitations to any of this? Apologies if this is not the perfect place to ask this question. I’m a lost old man. :-)

Yes, that is one of the features of being federated. Kbin and Lemmy and Mastadon (and others) can all federate with each other, so posts and comments are all shared.

Well, my understanding is that email is federated, and SMS text messages are federated, but it isn't easy to email a phone number, or send a text to someone's email. So I'm surprised that Kbin and Lemmy can talk to each other.

But I see someone else answered that Lemmy, Kbin, and Mastodon all speak the same underlying protocol, ActivityPub. Now it's starting to make sense.

but it isn't easy to email a phone number,

Mildly off topic, and showing my age a bit on this one but it 100% is easy, as long as the telco in question supports it.

I used to be with Koodo up here in Canada (albeit this was years ago) and the ability to send/receive emails via your phone number was trivial. Literally could email 5555555555[AT]msg.koodomobile.com and it would be received, and when you reply the other side gets the email reply.

Whether companies still do this on the other hand, is the question (that no one asked lol).

I think text to email is pretty universally supported. I work with clients who text my email address, and as far as I can recall I've always received the messages and been able to reply.

It's still a thing. At least with Gmail accounts:

https://support.google.com/fi/answer/6356597?hl=en

And you need to use the google messaging app on your phone. It probably bypasses texting and goes straight to the internet.
I remember seeing that as well in the US, but I think it was just too early in the internet phase and too odd to catch on. Then once smartphones became a thing it was pointless.
Yeah, however I think this doesn't mean email and sms share the same protocol like kbin and Lemmy. I am guessing that the service provider (koodo in this case) is serving as a relay, basically people email koodo, and koodo forward that email to your phone.
This is how I got ringtones I made onto my phone. I'd just attach the .wav file to my email and it would show up as an MMS.