Anti-Spam

Introduction to Spam

Unsolicited Bulk Email (UBE), also known as spam, costs organizations and individuals billions of dollars each year. It consumes time and resources while delivering content of limited, if any, value. Among the primary tools of spammers are third-party email servers with open relays. This means anyone can send an email through the server to anyone else, even if neither the sender nor the receiver has an account on the server. Spam can also come from authorized users with accounts on a server.

To help control spam, Ashland Home Net email servers are configured to perform a variety of tests that eliminate unwanted email.

Blacklists

When a sender's Mail Server attempts to connect to your Mail Server to deliver email, we first check the sender's Mail Server against our Blacklist of known abusers (Brute-Force Hackers, Email Harvesters, and High Volume Spammers) . If they are listed then the connection is dropped as if your Mail Server does not exist. We routinely block @ 8 million connections every day from a list of 127,000-500,000 known abusers that are continuously updated.

Identity

If they pass this primary test, we then say "HELLO" to the sender's Mail Server and ask them to identify themselves and who they are sending mail for. If the identity of the sender's Mail Server is not a FQDN (Fully Qualified Domain Name) or cannot be verified through a rDNS (Reverse Domain Name System) lookup then their email is not accepted for delivery. However, if the identity of the sender's Mail Server checks out as valid then the sender's address is also checked against a list of known Spam domains and email addresses. If the sender is listed then their email is not accepted for delivery. If they fail either verification then the sender should receive a NDR (Non-Deliverable Response) from their Mail Server telling them that the message was undeliverable due to Spam Filters. If, on the other hand, either the sender's email address or their Mail Server is recognized as "Trusted Sender" then the message goes straight to your Inbox.

Greylisting

If the sender's email address seems okay but your Mail Server does not recognize the sender as either a Trusted Sender or as having sent email to you in the past 288 days (10 months), then we ask the sender's Mail Server to please try again in 120 seconds. This waiting period is called Greylisting and is really effective at stopping Spam because most spammers do not attempt redelivery, whereas legitimate Mail Servers are required to attempt redelivery a minimum of 4 times. A two minute waiting period for an email from an unrecognized sender might seem to be an inconvenience but Greylisting can be 90% effective at reducing Spam as spammers have more than plenty Junk E-Mail to deliver elsewhere to bother returning 120 seconds later to deliver just to you.

Other Anti-Spam Checks

Once the message passes Greylisting, or is recognized by your Mail Server for having sent email to you in the past 288 days, then the message is subjected to 179 tests to determine if it is Spam (Junk E-Mail). Each test assigns the message a score, ranging from a maximum of -10 for each HAM (the opposite of Spam) and Whitelist checks it passes to 1-20 (with an average of 5-10) for each RBL (Realtime Block List), URIBL (Uniform Resource Identifier Block List), Checksum, Content Filter, or Bayesian/Statistical check it fails. After all of these tests are run the total score is tallied and an action is determined based on a scale of -100 to +100 as follows: