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HOSTING UK SPAM PROTECTION SYSTEM - TEST WE PERFORM. |
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Tests that we perform on e-mail |
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The spam filter performs a number of tests to check if an e-mail has come from known or listed sources of spam or on whether the headers of the e-mail are incomplete or have been modified in some way which is a good indication that the e-mail is indeed spam. A complex system of weighting is applied to all e-mail.
How WEIGHTING works.
All e-mail has 14 specific tests performed on it. Each of these tests assigns a weight to the e-mail depending on the perception of risk assessed in the test.
If the e-mail passes the test, the weighting is 0, however the REVDNS test (see below) has an assessed risk of 15.
The example below is from a genuine mail which failed a number of tests - we've blanked out the original sender details but it serves as a good example.
X-RBL-Warning: REVDNS: This E-mail was sent from a MUA/MTA XXXXXX with no reverse DNS entry.
X-RBL-Warning: WEIGHT10: Weight of 15 reaches or exceeds the limit of 10.
X-Declude-Sender: XXXXXXXXX@XXXXXXX.com [111.111.111.111]
X-Note: This E-mail was scanned by for spam.
X-Spam-Tests-Failed: REVDNS, WEIGHT10, WEIGHT15
If an email fails one or more tests a 'X-RBL-Warning' is added to the email header along with a weight associated with the failure.
As you can see, the mail was sent from a domain which did not have a valid MX entry in DNS as per RFCs which was enough to generate a weight of 15.
You would not normally see this when reading your e-mail but it can be viewed, for example in Outlook, by opening a message and then selecting VIEW and then OPTIONS from the menu.
There are five possible 'X-RBL-Warning' headers and weights that can be added to a message. These are shown on the table below. |
| Weighting |
X-RBL-Warning |
| 0-9 |
(No header added) |
| 10-14 |
X-RBL-Warning: WEIGHT10 |
| 15-19 |
X-RBL-Warning: WEIGHT15 |
| 20-24 |
X-RBL-Warning: WEIGHT20 |
| 25+ |
X-RBL-Warning: WEIGHT25 |
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Actions taken on suspected spam |
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| Although there are a series of actions we can perform on suspected spam, which include deleting the mail or returning it to the original sender, at this time we only stop mail that exceeds a weight value of 20 or if the mail is banned at spamcop. |
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Filtering your e-mail for spam |
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The weight you decide to filter mail on is decided by you, when setting up your filtering options - see Configuring Outlook rules for details of how to do this with Outlook XP
The full range of X headers added to email that can be filtered using email clients such as Outlook XP and Outlook Express are listed below. |
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Test Name |
Description |
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MAILFROM |
This test checks the SMTP envelope "Mail From:" address (which should be the sender of the E-mail) and makes sure that the domain name it is coming from is valid. |
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BADHEADERS |
This test checks the E-mail for illegal headers that are common in spam, but not common in legitimate E-mail. This test can catch about 50% of all spam, with the only false positives being mail that comes from broken mail clients. |
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SPAMHEADERS |
This test checks the E-mail for headers that are common in spam, but not common in legitimate E-mail. This test is very similar to the BADHEADERS test, except the problems this test looks for are not RFC violations, so there's a chance you could catch a small amount of legitimate E-mail. |
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ROUTING |
This test will analyze the route that an E-mail takes, and look for highly inefficient routing that is very common in spam. For example, an E-mail might get caught if it is sent from a dialup in the U.K. to another account in the U.K., but is routed through a server in China, but not if it goes from a mail server in China directly to a U.K. mail server. Not a reliable test outside the U.S. |
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REVDNS |
This test will check to see if a mail server has a reverse DNS entry. If not, it will fail this test. All Internet hosts are required to have a reverse DNS entry, although most do not. Most mail servers do have the required reverse DNS entry, but there are huge numbers that do not, so it is likely that this test will catch a lot of legitimate mail. A warning in the headers might be appropriate for this test. |
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PERCENT |
This test will catch all mail with "To:" addresses that contain a percent sign. The percent sign indicates an outdated routing method that can be used by spammers to bypass closed relays. |
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WEIGHT10 |
This test will catch E-mail that has a total "weight" of at least 10. This will occur if the E-mail fails several different spam tests. |
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WEIGHT15 |
This test will catch E-mail that has a total "weight" of at least 15. This will occur if the E-mail fails several different spam tests. |
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WEIGHT20 |
This test will catch E-mail that has a total "weight" of at least 20. This will occur if the E-mail fails several different spam tests. |
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WEIGHT25 |
This test will catch E-mail that has a total "weight" of at least 25. This will occur if the E-mail fails several different spam tests. |
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Note: As we develop and refine this system these weights may change and so you should check this page frequently to be sure. |
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The technology behind our tests |
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| The spam tests we perform are generated by DECLUDE JUNKMAIL. Declude is an acknowledged leader in e-mail filtering technology. |
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Peter Jackson has been extremely helpful, answering my inane questions and following up on emails ve... (cont'd)
TG
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