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

...@gmail.com and ...@Gmail.com 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.

• test@gmail.com and test@Gmail.com should be the same account.

  test@gmail.com and Test@Gmail.com should be different accounts.
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@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