This happens to me in the initial setup wizard when taking a search, and making it into an alert. It happens specifically if I have an address that has the form "email@example.com", something normal like firstname.lastname@example.org works fine. I suspect it's the subdomain in the email address. A workaround seems to be to skip that part in the wizard, and go to manager to edit the alert. It seems to access it just fine.
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