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I've used a catch-all email for about 14 years now, I have no idea what you're talking about as this has literally never been an issue.
Back in the 1990s, a spammer who knew example.com existed would bulk e-mail a dictionary of prefixes - andy@example.com, bob@example.com, claire@example.com etc etc in the hopes that some would get through. As such, a catch-all e-mail address was a sure way to get hundreds of copies of the same spam e-mail. And since most people who wanted a catch-all address were doing it as part of a strategy to get less spam, that…
My domains are not really "out there" in any big way though, so perhaps I've just been lucky?