For anyone who thinks that may be a hand wave, there isn't a standard way to normalize email addresses. If you're building to the spec, then the local part can be processed case-sensitively, so Django lowercases the part after @ only. Others strip out stuff like gmail's +tags and really get into the weeds of how different email providers process emails.
In my mind, the "Right Thing to Do" would be to follow the precident established by OpenPGP's `.well-known` email-hashing in Web Key Directory (not the prefix of course, and barring technical arguments justifying deviation, which may be considered on merit).
> SHA-1 hashed and z-Base-32 encoded [to distinguish it from a fingerprint]
> The local part is always lower-cased before the encoding. [...] A common example for case-insensitivity are visiting cards which capitalize the canonical lowercase mail address for easier reading.