Except there is no need for that whatsoever.

1. If you only want email relays to make onboarding easy, check how DeltaChat works.
2. If you want email to not depend on ICANN then the solution is fixing DNS not fixing SMTP, SMTP is fine. Nostr can't replace ICANN because there is no way to lookup a key to get MX records. I am working on this if you care at https://github.com/Nuhvi/mns

Of course if the purpose is to get funding from Nostr focused foundations, then it is pointless to argue about technology.

Email isn't only successful just because network effect. In fact if it wasn't really good already, it would have been replaced at least partially by phone numbers, which is not only earlier than emails, but also more prominent in chat apps which are increasingly more prominent in commerce and many other access context where you join the thing just by joining a group chat.

I am singing the praise of reliable and simple messaging, whether that is reliable messaging of a server with TCP/HTTP or a more intermittent entity like the case in Email, and indeed SMS or other chat apps.

Email is indeed benefiting from network effect, but it is also not the first solution, it was just the first good enough solution. And indeed any upgrades that I find worthwhile for Email, happen entirely at the DNS level, not the email format or protocol.. that shit is really truly good enough...

Hell I am using a Signal alternative that is entirely on Email protocol and it is working like a charm, and it is not even using Email as a thing you already have, it creates whole new account in the background... It just uses SMTP because SMTP is simply good enough

No, OP_CAT would let sidechains start permissionlessly with blind merge mining and optimistic bridge. But even string concatenation is too hard to do on Bitcoin, which is insane given that everyone wants post quantum now, which is orders of magnitudes harder.

Filtering by tags is worthless for anything but broadcasting, but we established that even Nostr apps are mostly going in direct mailing direction with communities and the like.

To that extent Chatmail relays are doing way better job than Nostr, probably more relays too.

You are under the impression that only Nostr relays do that. That is false, and they aren't even the best at it. But I am also not interested much to prove this so use whatever is working for you

1. Nostr doesn't magically solve anything here it just abandons the very minimal expectations that your data doesn't get deleted.
2. You can and people do run their own SMTP servers
3. Many people pay for paid email especially privacy orientated
4. Many competitors offer 15GB for free, to attract users that upgrade to premium.

Email is the most competitive service out there in the modern age... And it can only get more competitive if you add sovereign domains so you an exit from one service to another without losing your id.

If I know that I only ever want to do small communities, and private communities, or at least communities that don't care about broadcasting as widely as possible, I wouldn't care about Nostr at all, I would just focus on adding sovereign domains, ones that are easy to provision to users, to what we already have; emails, mailing lists, and some work on Drives, encrypted or just WebDav/S3-like API.

That is basically using Email to do what Nostr relays do, but the difference is that you don't add anything more than you absolutely must; usuable sovereign domains. The rest is good enough.

You can argue that you can repurpose Nostr relays to do what Email servers already can do, but then the same applies to S3 providers, and it is not clear why would I bet on Nostr relays and query language, Vs betting on S3 API and SDKs or Emails and their countless tools.

As if what I would do if I absolutely insist on using Nostr, then I would probably go all in on inboxes and outboxes and relays with serious data retention and storage quotas and access control and the whole thing, until they are indistinguishable from Email... Except for all the redundant effort for no reason.