Unknown Sender Delay – aka Greylisting

If this is enabled on your domain then our system will deliberately delay emails from unknown senders for a short time – normally only a few minutes. The exact time depends on the sending server. This short delay results in a very effective spam filtering mechanism and we strongly recommend you leave this feature enabled. Once an email is accepted from a new sender, future emails from them will not be delayed by this feature.

This feature is also known as Greylisting and many other providers also employ Greylisting as a way to reduce unwanted emails. Our implementation of Greylisting is heavily customised to increase effectiveness and reduce impact on legitimate emails.

Senders with valid SPF records are not subject to the Unknown Sender Delay.

There are rare occasions where the sending server is misconfigured and does not retry delivery after the initial delay – this can result in a bounce message to your correspondent (who is trying to email you). If this happens, they should refer the matter to their email administrator as there is nothing we can do to help.

How to fix:

• It is technically possible to disable this feature, but it is a highly effective spam filtering measure and because it rarely causes a problem, we strongly recommend you do not disable it. Your email administrator is able to disable this feature.