Changes in version 22.214.171.124 (November 12, 2008)
NDR Codes - Alligate will now return NDR codes for message refusals and errors. The NDR codes used are in the MS Exchange standard 4.x.x and 5.x.x format. Where possible we use standard responses. The standard responses however do not provide for Alligate's additional refusal mechanisms, so we are using some non standard codes. The complete list of codes we return and the conditions that apply is available here. This will help administrators more easily determine why messages were blocked when they receive reports of errors without extensive research into the logs.
Temporary Blacklisting - In previous versions, senders could be placed on a temporary blacklist if the sender attempted to send messages to a user defined number of invalid recipients. This feature is designed to stop dictionary attacks.
When using greylisting, the greylist check is done before the recipient validation. So if the sender fails greylisting, the invalid recipient test would never occur. During a dictionary attack there was no mechanism to stop them if the recipient address failed greylisting.
A new feature was added to temporarily blacklist IP addresses if they fail a user defined number of greylist checks. To help prevent false positives, you can also specify that at least one DNSBL hit is required before the sender IP is placed on the temporary blacklist. Please see the screenshot below: