[TRI-2630] Logging in with the same email but different case creates a new account

[Matt Aitken]

If you login with [e-mail] and [e-mail] you will create two accounts.

_{From SyncLinear.com | TRI-2630}

[Hunain Ahmed]

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

[Matt Aitken]

[e-mail] and [e-mail] 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.

[Matt Aitken]

• [e-mail] and [e-mail] should be the same account.
• [e-mail] and [e-mail] should be different accounts.

[Matt Aitken]

@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