TIL: The part of an email address before the @-sign, known as the "local-part", is technically case-sensitive, so the emails: jane@example.org and Jane@example.org could both technically exist.

https://www.rfc-editor.org/rfc/rfc5321.html#section-2.4

However, any email server that actually allows for this style of case-sensitive local-part is going to:

a) create a world of pain for the person using the email with upper-case characters, since most software will lowercase compare emails for account registration/login

b) have utter chaos with regards to misaddressing and impersonation. "Oh, you're jane@example.org? No, I'm Jane@example.org"

Like, who really thought case-sensitivity here was a good idea to allow, and why?