In regards to Greylisting, what is its primary strategy?

The primary strategy of greylisting is to temporarily reject messages and wait for retries. This approach works based on the understanding that most spam is sent in bulk and relies on automated systems that will not retry sending an email if they encounter a temporary failure. By initially rejecting an incoming email from an unknown sender, greylisting gives the legitimate sender's email server a chance to retry sending the message after a brief delay. If the server attempts to resend the email within a specified time frame, it is typically recognized as genuine, allowing it through after the retry, while most spam servers do not make that second attempt. This helps to significantly reduce the volume of unwanted spam that enters the system, improving overall email security and reducing unnecessary load on the email infrastructure.