Using junk mail filters in Thunderbird
This article describes what you can do to reduce the impact of spam, which is on the increase and is causing problems for e-mail users everywhere. There are several strands to our anti-spam effort.
Most productive of all is the use of internationally maintained blacklists of addresses that are know as originators of spam. All messages which originate from a blacklisted address are rejected by our mail servers – at present we are rejecting in this way over half the messages that reach us.
We use the SpamAssassin software to subject the contents of the remaining messages to a series of tests and when a message is recognised as spam, the {Spam?} flag is placed in its Subject line. Users who wish to do so can set up a filter on the server to discard all messages addressed to them which are flagged in this way. There is a small risk of discarding genuine messages but many people feel the risk is worth taking. At present the success rate of the SpamAssassin tests is less than it was a month or so ago. We estimate that we are currently flagging about 70% of spam. Before October the success rate was over 90%; we are working on the problem and hope to get back to this level before long.
You can supplement this effort by using filters in your e-mail client (Thunderbird, Eudora or WebMail, for example). We have always advised users not to try to create their own filtering tests in their e-mail clients, because it is very unlikely that you will do better than the authors of SpamAssassin. However some e-mail clients have a facility for creating their own tests for spam. You can ‘train’ the filters by confirming or correcting their attempts to identify spam. Once they have been trained these adaptive filters prove surprisingly effective.
In Eudora this facility has always been restricted to the paid-for version of the software. In Mozilla Thunderbird the adaptive junk filtering facility is part of the standard (free) package, and it is one of several reasons why our users are beginning to move from Eudora to Thunderbird. Users have reported that after a few days they are finding that the filters are catching 90% or more of their spam. Combined with the centrally managed spam filtering efforts, this leaves them with comparatively little spam to deal with by hand.
Instructions for using the adaptive junk filters in Thunderbird are given on the IT Services web-site. Note that if you use this facility you should not tell Thunderbird to delete the messages it identifies as spam, but to place them in a Junk folder. This enables you to run your eye down the list of messages to see if any genuine messages have been caught by the filter. Thunderbird makes it easy for you to mark them as ‘not junk’ and the filters will learn from their mistakes. After a few days you will find hardly any genuine messages in your Junk folder, but nonetheless it is prudent to check every so often. If you become aware that a message has been sent to you but seems not to have arrived, your Junk folder is one place to look, in case it has got there.
Instructions for downloading and installing Thunderbird are available on the ITS web site. It is easy enough to install and to import your Eudora settings and Eudora mailboxes.
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