Unique is case sensitive but email domain isn't
Email domains are not case sensitive but the unique constraint in Django is, so EmailField(unique=True) allows for duplicate emails to be registered in the database
"Email domains are not case sensitive"
https://django-improved-user.readthedocs.io/en/latest/email_warning.html
RFC 5321 states that the mailbox in mailbox@hostname of an email format is case-sensitive. ANDREW@example.com and andrew@example.com are therefore different email addresses (the domain is case-insensitive).