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I would be curious to know if there is some credible A/B testing showing that for a relatively unknown new product blocking Mailinators and it’s kin somehow results as a better conversion?Well, there's always this: https://articles.uie.com/three_hund_million_button/ -- trigger warning: that page has annoying delayed-by-few-seconds modal popup that begs you to subscribe and, incidentally, hand out your email address; the irony must have been lost on their marketing folks.
Unless your business is REQUIRED[×] to have user details on file, putting any kind of friction on the user's action path is equal to voluntarily giving up sales. No, I don't want yet another account on your shitty website, no matter what it sells to me. If I end up coming back often enough, then I may, voluntarily, create an account. But if your site requires to create one up front, I'm incentivised to take my business somewhere else.
The worst offenders try to do email domain TLD matching against country of residence. I've seen it only twice, but it's such a user-hostile pattern that it has seared itself to my memory (while mercifully having relieved me of the memory of where I ran into it).
×: cough gambling, financial services, insurance, etc.