Message scanning is a new feature introduced in Alligate 3.7.8.x. It gives you the capability to assess penalties against messages for various violations or suspicious elements of the message transaction.
Penalties are assessed at various points during the process of receiving the message. If the point score is high enough after receiving the HELO or EHLO command the message will be refused with a 550 response at that point and the connection will be terminated. If the message has not been refused by the time the entire message has been received but not yet saved to disk, and the point score at that time is high enough to warrant refusal, a 550 response will be issued and the message will be refused.
This feature is provided to provide additional protection at the Gateway level from spam that can be identified through a series of reliable tests. Messages should never be refused based on failing a single test, nor should they be refused after failing 2 or even maybe 3 tests. Alligate provides numerous tests that allow you to set reasonable scores that accumulate as the message transaction progresses so that obvious spam can be eliminated before entering the network.
Message scanning features are arranged in four categories. General scan options, envelope scan options, header scan options,and message scanning. All four categories of scan options are utilized to determine the likelihood that the message is spam.
One useful feature of the new message scanning system is the ability to utilize external DNS blacklists (DNSBL). Alligate will allow you to define two external blacklists to use when checking a message. The use of these lists is intended to provide additional confirmation when a spam is suspected. There are several reliable DNSBL services available that have a very high accuracy rate. The use of these services can significantly increase the reliability of message rejection based on message scanning.