Restricting accepted addresses to "normal" ones is common sense, not a falsehood. In the case of a@a.com, that's just someone not wanting to give an email addr

Restricting accepted addresses to "normal" ones is common sense, not a falsehood. In the case of a@a.com, that's just someone not wanting to give an email address. You can block it with validation rules, but they'll just use some random but not real address like noemailforyou@gmail.com instead. The validation achieves nothing except annoying the user, really annoying anyone whose legitimate address is blocked as a false positive, and makes your email address database harder to clean up if you ever want to send an email to everyone. Blockimg emails because they're "not normal" is validation theatre. It doesn't stop anyone nefarious or who wants privacy, it doesn't stop spammers, and it does stop rare cases of people with weird email accounts.