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The fastest and most efficient way to remove duplicates from a list while preserving the original order in Python is to use a set for checking membership and a list for preserving the order.

Here’s a clean and efficient implementation:

def remove_duplicates(emails):
    seen = set()
    result = []
    for email in emails:
        if email not in seen:
            seen.add(email)
            result.append(email)
    return result

Why this works:

• set is used for constant-time (O(1)) lookups to check if an item has been seen before.
• list maintains the order of the first occurrence of each email.
• Time complexity: O(n), where n is the number of emails.
• Space complexity: O(n) for the seen set and the result list.

This method is ideal for a list of 2 million items. It's fast and memory-efficient for most modern hardware.