Sure, but the person I was replying to seemed to imply that there is some lack of interoperability of apps in the Fediverse when the whole point of the Fediverse is interoperability not just between the different apps, but even different servers sharing the same protocol
They seem to have misunderstood that just because .ml decided to defederate from Kbin, they will never be able to interact with Kbin posts and comments on Lemmy when in reality you can just sign up on another instance and it works just fine. Or you host your own, and you control what you see
Gmail itself, in that situation, is just a frontend to the mail server. You can use the same domain, on any mail server, with any frontend, and it would work just as well. It's just that Google Workspace apps are familiar to most users. But even then, the industry leader is Microsoft with their Office Suite which is yet another option