Scam-grey is an email filtering software that blocks email messages from MS Windows computers that are identified as spam.
Scam-grey operates by generating a temporary error message when a Windows host makes its first delivery attempt. After a certain delay period provided by the software, subsequent delivery attempts are allowed through. This is because virus, trojan-infected hosts, and zombies are not designed to retry the delivery after a temporary failure.
Furthermore, Scam-grey pairs the helo string and the IP address of the sending server (host) as a record and returns a temporary failure (SMTP code 450 extended code 4.7.1) if the host is greylisted. The record expires if there is no connection for the matching record within the next 24 hours.
To view a sample of mail servers which are currently greylisted, click here. Additionally, you will require sendmail version 8.12.x or higher, milter library and development kit installed, and P0F.
In the latest release of Scam-grey, several updates have been made, including a change in the SMTP message to show the actual delay for each connection. The software also now comes with an added feature to make logging less verbose, and the ASN lookup takes precedence over the regular expressions used for whitelisting.
Version 1.6.3: N/A