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Our Term of the Week series explains key marketing terms in about 150 words. This week, it’s greylisting.

Anti-spam software is more effective than ever, making consumers happier, and helping legitimate senders reach the inbox. One weapon in the anti-spam war is greylisting. Even though you’re probably not a spammer, learning how greylisting works can help you make sure you are not wrongly identified as one!

How does greylisting work? When a mail server using greylisting detects an email coming from an unidentified or suspect sender, it will stop it and return a temporary error. It will also record the timestamp of that attempt to send. Then, the mail server will monitor to see if further attempts are made by the same sender within a specified time period. For instance, no sooner than 30 minutes but no later than 6 hours.

This is where spammers and legitimate senders are different. Spammers use the fewest resources possible, so they don’t bother with configuration for further attempts. A legitimate sender’s server will automatically resend the email several times, until it’s eventually allowed to pass through to the inbox. The mail administrator will handle this configuration for you, so you only need to worry if you notice major deliverability issues. If this is the case, you should investigate thoroughly with your ESP.

You can read the advanced explanation, or if you have a term you’d like explaining, simply leave a comment below.