Who altered my mail?

DSL Only has implemented a system to combat spam, based on software called "SpamAssassin". This system examines mail and may alter messages that it believes to be unwanted.

Why was the e-mail altered?

Each incoming e-mail is scanned for clues that it may be spam or a virus. If it is determined that it's likely to be spam, it is altered to clearly reflect this, so that you -- the user -- can decide whether to delete or keep it.

Because viruses represent more risk, the system will try to remove all suspicious content from a a message if it believes that the message contains a virus. It will leave the basic text of the message, so you can see what the sender was trying to do, but the attachments will not come with the message. In the interests of privacy, we do not keep copies of these attachments.

If you have concerns about the policies for scanning and tagging spam and viruses, please contact support@dsl-only.net. We can disable spam or virus scanning on your mail (or both) if you wish. The filters are intended as a convenience for you, but if don't want them, we disable them for your mail.

But The Message Was Not Spam!

Occasionally the system will be tricked into making a "false positive", and tagging a message which is not actually spam at all. Since spammers try to disguise their unwanted, unsolicited ads, as legitimate mail, the system has to try to work it out -- and it's not always easy to do.

If this does happen to you, we want to know about it, so we can try to improve the system and make it happen less often. Please contact support@dsl-only.net (and understand that we will probably need a copy of the message if we are to learn anything from it).

Why do I still get spam that isn't marked?

Determining which messages are spam and which are legitimate is a very difficult job for a computer. SpamAssassin looks at the message from lots of angles and tries to come up with a number, the "spam score", indicating how likely it is that this message is spam.

Because the consequences of accidentally marking even a single legitimate message as spam are high, SpamAssassin errs on the side of caution: it doesn't tag a message unless it's highly confident in its rating. 100% accuracy in tagging spam is not a realistic goal, so we are just trying to get as much as we can. It's a game of percentages.

Unlike with "false positives" above, it is not helpful for us to look at individual spam messages to adjust the system. SpamAssassin is trained statistically from time to time, on massive collections of collected spam, together with collections of legitimate mail. Trying to adjust the system for a single kind of spam, even one you might be receiving over and over again, will actually hurt the overall accuracy of the system, so we don't train it that way.

But I Don't Get Much Spam!

Count yourself lucky, then! The longer you have your e-mail address, the more spam you will get.

It may not be a problem for you -- yet -- but others find it very frustrating. Some recent research has indicated that on average, as much as 80% of the e-mail travelling around the Internet is spam; quite a few old-timers who've used the same address for years, get 30-50 or more spams a day.

You say that 80% of the messages out there are spam, but your filter only tags half of the spam I receive. Isn't that a poor performance?

You might be tempted to think so, but there is more going on behind the scenes.

Before the message is even handed to SpamAssassin for scanning, our mail servers look very aggressively at the the way the message comes in to us. We use a variety of checks to try to ensure that the sender's address is legitimate, that the computer sending us the message is really who it says it is, and so on. Using this circumspect procedure, we are able to reject around 70% of incoming mail as bogus before even looking at the content.

What this means to you is that the spam you receive in your mailbox (both tagged and untagged) is only a small fraction of the spam people are trying to send you. We are able to identify most of it with enough confidence to reject it outright. The rest is scored with SpamAssassin and delivered to you for the final judgement. Since we've already thrown out the 'easy ones', SpamAssassin's job is that much harder; it only sees the spam that isn't obvious.

We do things this way because we want to shield you from as much spam as possible, but we want to avoid blocking any legitimate mail if possible.

What about viruses and other malicious software?

In addition to scanning for spam with SpamAssassin, we have added virus scanning to the capabilities of our filter using ClamAV. This scanner can capture most viruses before your computer is exposed. It will also recognize many kinds of "Phishing" and other malicious content.

While it is our hope that the scanner will save you time and headaches, we cannot guarantee that it will recognize all viruses, and there are many other kinds of malicious software which do not need e-mail to spread. It is still important that you install current antivirus software on your computer to protect you from these other kinds of risks.

I received a message saying that it was scanned for viruses and found clean, but on the same message it says that a virus was found. What's going on?

The message is surely bogus. Legitimate virus scanning software never marks a message as 'clean'; it only knows when it doesn't find anything, and the right way to say that is to say nothing. A real virus scanner only speaks up when it finds something it doesn't like.

Viruses commonly lie, claiming that they are verified 'virus-free'. They even sometimes look at your own e-mail address and make up some likely-looking wording about being scanned by your provider (us). Don't be taken in.

We try to help by putting consistent marking on messages we think are viruses (and removing any attachments we think could be dangerous). But the bottom line is: if the message says it's a virus, or says it's virus-free, it's a good bet that it's a virus and that you don't want anything to do with it.

How Can I Turn It Off?

If you just want all your mail, unfiltered, send a message to support@dsl-only.net and ask for your address to be removed from the service.

What is SpamAssassin?

SpamAssassin is a program which looks into messages and attempts to recognize spam. More information here.