Greylisting: why an email sometimes arrives a few minutes late

Greylisting is a way to stop spam. When a message comes in that looks a bit suspicious, our mail server tells the sending server: try again in a few minutes. A normal mail server does this automatically, and the message still arrives. Many spam programs never try again, so that spam doesn't get through.

When does it happen?

Our spam filter gives every incoming message a score. Only a message with a doubtful score, but which isn't clearly spam, is briefly held back like this. Most mail from regular senders scores low and arrives right away. Mail you send yourself through our servers, logged in with your email address, is never delayed.

Once a sender has gotten through, the next mail from the same sender via the same server usually isn't delayed again.

What will you notice?

The message arrives later. The delay is at least 5 minutes. Exactly how long depends on the sending server: most try again after 10 to 30 minutes, some only after an hour. You don't need to do anything. The sender doesn't get an error message, because their server simply tries again.

Is a mail not arriving at all, or always arriving late?

• The sender gets an error message with 451 or Try again later. In that case their server doesn't try again. This mainly happens with a custom script or a poorly configured service that sends mail itself. Have the sender send through a regular mail server (SMTP), which does try again. You can read what these codes mean in Mail delivery failed: how to read the error message and what the codes mean.
• Mail from a regular sender always arrives late. In that case their mail keeps getting a doubtful score. Usually something is missing in the sender's SPF, DKIM or DMARC. Ask the sender to check this, for example with www.weboke.nl/en/email-check. Once it's set up correctly, their mail scores lower and is no longer delayed. Explanation for the sender: My email isn't arriving or ends up in spam: how to find out why.

Greylisting can't be turned off per mailbox. It's part of the server's spam filter and stops a lot of spam before it even reaches your mailbox. You can read more about how our spam filter works and how to train it in Spam: how WebOké stops it, and how to train and test the spam filter.