Delete Duplicate Emails

You are tasked with cleaning up a dataset of email addresses. In many real-world scenarios, data can become duplicated, leading to inefficiencies and incorrect analysis. This challenge requires you to process a list of email addresses and remove any duplicates, ensuring each unique email appears only once.

Problem Description

Given a list of email addresses, you need to return a new list containing only the unique email addresses from the original list. The order of the unique emails in the output list does not matter.

Key Requirements:

The function should accept a list of strings, where each string represents an email address.
The function should return a list of strings, containing only the unique email addresses from the input.
Case sensitivity for emails should be ignored (e.g., "Test@example.com" and "test@example.com" are considered duplicates).

Expected Behavior:

If the input list is empty, an empty list should be returned.
If the input list contains only unique emails, the output list should be identical to the input (though the order might change if your implementation naturally reorders).
If an email appears multiple times, only one instance of that email should be present in the output.

Edge Cases to Consider:

Empty input list.
List with all identical emails.
List with mixed case duplicates.
List with emails containing special characters (although for this problem, we assume standard email formats and focus on duplicate detection).

Examples

Example 1:

Input: ["john@example.com", "jane@example.com", "john@example.com", "peter@example.com", "jane@example.com"]
Output: ["john@example.com", "jane@example.com", "peter@example.com"]
Explanation: The email "john@example.com" appears twice, and "jane@example.com" appears twice. After removing duplicates, we are left with three unique email addresses. The order of the output can vary.

Example 2:

Input: ["test@domain.com", "Test@domain.com", "ANOTHER@domain.com"]
Output: ["test@domain.com", "another@domain.com"]
Explanation: "test@domain.com" and "Test@domain.com" are considered duplicates due to case insensitivity. "ANOTHER@domain.com" is unique, but its lowercase version is returned.

Example 3:

Input: []
Output: []
Explanation: An empty input list results in an empty output list.

Constraints

The input list will contain between 0 and 1000 email addresses.
Each email address will be a string with a length between 5 and 255 characters.
Email addresses will adhere to a generally valid format, focusing on the duplicate removal aspect rather than strict email validation.
The solution should be efficient, aiming for a time complexity that scales well with the number of emails.

Notes

Consider how you can efficiently keep track of emails you have already encountered.
Remember to handle case insensitivity correctly. You might want to normalize the emails before comparison or storage.
The order of emails in the output list is not specified, so you have flexibility in how you present the unique emails.