What is one key characteristic of greylisted messages?

Greylisting is a process used in email security to mitigate spam and unwanted messages. A key characteristic of greylisted messages is that they are temporarily rejected by the receiving email server when they first arrive. This temporary rejection occurs because the server will not recognize the sending server as trusted at that time, allowing the process to act as a deterrent for spammers who often do not attempt to resend messages. The intention behind greylisting is to encourage legitimate email senders to retry sending their emails after a short interval, as most legitimate mail servers will attempt to resend the message after a few minutes.

The effectiveness of greylisting lies in the behavior of spammers. Many spam servers do not retry sending emails after a rejection, allowing the legitimate emails from known senders to come through when they are resent. Thus, the temporary rejection serves as a filtering mechanism that helps reduce the influx of spam into the inbox, making it a smart approach in email security strategies.