The correct answer is All of the above.
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While massive quantities of spam are sent, the success rates for spam are indeed tiny, meaning that the overall profit is limited.
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Anti-spam laws and automated spam filters have significantly reduced the amount of spam traffic, though it still remains a persistent issue.
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Unsolicited marketing emails generally must include an unsubscribe mechanism, and it is required to honor those requests within a certain timeframe, typically 10 days.
All statements are true, making "All of the above" the right choice.