Particularly Lemmy because Lemmy admins have fundamentally broken the idea of federation with defederation. It generally doesn’t matter what email you use or what email the receiver uses, baring more niche services. It does actually matter what instance you’re on.

You've probably never tried using email outside of Google, Outlook, Yahoo or Proton but let me tell you it doesn't just work. A lot of the servers have been blocked by the big first 3, sometimes soft-blocks being redirected to the Spam folder, but often times hard blocks where they don't get through at all. So it very much does matter what email service you do use, as many of the smaller ones and domains you might obtain to set up your own have been defederated, much more aggressively might I add. It doesn't take much for a domain to end up on spamhaus' or other spam lists, and it's a big pain to get them off said lists.

Let's compare with Defederation of activitypub services (because Lemmy devs didn't invent the idea of deferation, it's part of ActivityPub standard and is a thing on all activitypub platforms), something that typically happens when a server is spamming, spreading violent or hateful messages, or otherwise engaged in unproductive or harmful behavior (i.e. trolling, rudeness towards others, etc.). We don't use spamhaus or a similar equivalent service to filter "spam" automatically, much of it is done by server admins themself, there are tools like Fediseer meant to keep track of instances which are trusted as well as identifying known bad actors, but since this is community driven and not monolithic it is different from spamhaus and the like.

In all honesty the Defederation boogeyman is a very stupid argument, especially when comparing it to email which has ironically been hit the hardest by it. It has effectively been reduced to a handful of big players while all the other smaller ones out there find themselves unable to compete. Meanwhile on the activitypub side defederation is still an issue but it is a minor one and is limited to edge cases or bad behavior. One thing that is important to note, and why it isn't talked about more frequently to other people is this. When people invite others to join the Fediverse, they naturally assume the people who are joining are NOT trolls, alt-right sociopaths, neonazis, pedophiles, spammers, etc. and thus are not likely to have their accounts banned or the servers they start get widely defederated. If you are one of those people chances are you aren't the target demographic for most fediverse servers out there, and thus you will face friction, bans, and mass defederation because people do not want you in their spaces or to listen to your dogshit propaganda.

The Fediverse was never about freeze peach, it's about collaboration and cooperation between services, and most services do not want to collaborate with people who are assholes. The people still claiming that it is for free speech are lying or misinformed, because on most servers if you speak your mind and say things that are unacceptable or evil, there will be consequences. That means bans from those servers or defederation if you run your own.