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An update on my question.
A few hours ago, I attempted to answer the question of whether mods actually ever emailed b& users for questions. So I got myself banned for 7 days and appealed by asking said question. The ban appeal ended up getting reviewed and accepted with no email.
My personal thought is that the email field must just be a leftover from times past or, if the email field does actually work, it's a hassle to use.