Handling SPAM – How our System works

The J T Response email system checks for viruses and SPAM on all incoming and outgoing emails.

Viruses

All emails are scanned for viruses and our virus database is updated regularly. Any emails that we find contain a virus are automatically deleted. However, we can only block the viruses that our system knows about, so there is a small chance that the occasional virus may sneak through, so we would recommend that you still use a virus checker on your computer: it is best to play safe.

Spam

We deal with spam in two different ways: Black Lists and Content Scanning.

Black Lists

We use several services that keep black lists of servers that have been reported for sending large quantities of SPAM. These have been verified as persistent SPAM senders. We delete all emails coming from these servers.

Content Scanning

Our system scans the headers and contents of all emails, and uses a wide variety of tests to decide if the message is SPAM. While this system is very accurate, it does have the occasional false positive. This is why we do not delete these emails: We don’t want to delete an important email by mistake. Instead, several headers are added to each email to allow you to use your email program to filter them.  Here is an example:

X-Virus-Scanned: Debian amavisd-new at jtresaa14.miniserver.com
X-Spam-Flag: YES
X-Spam-Score: 17.689
X-Spam-Level: *****************
X-Spam-Status: Yes, score=17.689 required=6 tests=[BAYES_99=3.5,
	DNS_FROM_AHBL_RHSBL=2.699, FROM_12LTRDOM=2, HTML_MESSAGE=0.001,
	HTML_MIME_NO_HTML_TAG=0.377, MIME_HTML_ONLY=0.723,
	RCVD_IN_BRBL_LASTEXT=1.449, RCVD_IN_PBL=3.335, RCVD_IN_RP_RNBL=1.31,
	SPF_NEUTRAL=0.779, SUBJ_ALL_CAPS=1.506, T_RCVD_IN_SEMBLACK=0.01]
	autolearn=spam

These have the following uses:

• X-Virus-Scanned
  Confirms that the email has been scanned

• X-Spam-Flag
  Set to YES if the system has identified the system as SPAM

• X-Spam-Score
  The higher the SPAM score, the more likely it is to be SPAM.
  A score greater than 5 is normally been considered to be SPAM.

• X-Spam-Level
  This is similar to X-Spam-Score. There is an * for each whole number of the Spam Score.
  This makes it easier to filter email in some email programs.
  e.g. If you want to filter emails with a spam score of 6 or higher, you could match on 6 *’s

• X-Spam-Status
  This is for information only. It shows the checks that have been matched to produce the Spam Score.

In the near future we will be adding articles to explain how to use filters in various popular email programs.

Search Posts: