It seems like an alternative might be something along the lines of this, just a rough sketch

- Alice wants Bob to notify her about something

- Bob advertises an email address specific to that something

- Alice creates a disposable email address and requests that Bob notify her about that something at that disposable email address

- Alice only accepts emails to that address from Bob's something-specific email

- Once Alice receives an email from Bob's something-specific email she discards the disposable email

Email is very hard because all the big providers want to defederate from all the single-user instances.

You can use something like ntfy.sh, where you create a channel on a public relay and do pub/sub