@matt-aitken kindly assign this issue to me, would like to contribute.

[email protected] and [email protected] can be treated as equivalent because DNS specifies that domain names are to be compared in a case-insensitive manner. But the same is not true for the user/mailbox part of an address, that should actually be case sensitive so we should create multiple accounts for those.

• [email protected] and [email protected] should be the same account.
• [email protected] and [email protected] should be different accounts.

@hunxjunedo I've assigned this to you 👍

I've also added some more comments above about what exactly should cause a duplicate and what shouldn't