Mail delivery delayed

I received this bounce email message: Delivery delayed. What does it mean?

Don't worry! This message means that your recipient is using an antispam measure called greylisting. This will slightly delay the delivery of your message, but your email will reach its destination in a short while.

You do not need to do anything. Do not send your message again. It's not necessary.

Sorry for any inconvenience. This is a very effective antispam measure used by many mail servers, and supported by DeskNow, the mail server used by the recipient of your email.

Please do not contact us asking about this delayed delivery message. Instead, if you're unsure, contact your mail administrator.