Greylisting is an effective tool to stop spam by sending a temporary fail back to the sender of the message. If the sender is sent via a valid MTA, the message is re-sent and MWES will let it through. If the message is not sent from a valid MTA it is not delivered and left in the MWES greylisting quarantine area.

Greylisting is enabled by default in Settings >> Filters >> Settings

NOTE: Valid messages can be delayed by up to 15 minutes using this method since the sending MTA has to re-send the message. You can always check the Email>>Quarantine area to see which messages are due to be resent, and thus rescue them in which case they will be added to an internal IP Whitelist. See below, the light grey message at the top is within the 15 minute time period to be re-sent. Once an email senders email has been delivered once, they are let through instantly the next time they send an email.

NOTE: Enable SPF (Settings >> General), so email is checked against SPF records and if matched successfully it bypasses greylisting.

Users can move their mouse over the subject line to view the body (first 200 characters by default - preview length can be changed in Settings>>General)