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Email discussion lists for the UK Education and Research communities
JISCmail Newsletter Issue 2/03

Do you wish you could stop certain types messages appearing on your list ?

You can, with content filtering, list owners can block some messages and send a mail to the poster saying why they have been refused.

However, there are measures which all list owners should use to prevent unwanted mail being sent to the list in the first place, which is preferable to blocking it once its received. The biggest problem most list owners face is UCE (unsolicited commercial email) or spam as its universally known. The best technique we have for combating spam is to only allow postings to a list from list members, as most serious spammers don’t join our lists to do their spamming. This is achieved by setting send=private in the list header. All new lists have this as the default so there is no need for any action if you wish to set up a list or yours is a recent list.

Anotherá cause ofá unwanted mail is out of office replies (ooo messages). With version of 1.8e of listserv, which we installed back in July 2002, there is a feature which normally recognises ooo messages and blocks them. (Incidentally, this works on identifying the words precedence=list in the mail header, which is set in most ooo messages.)

Finally, all lists can be set up as reply=list or reply=sender, depending of course on to whom replies to any posting should be sent to. Reply=list is fine if you really wish everyone to receive everything, but often people do reply to the whole list when they really just wanted to reach one person, or there is often a flurry of ‘me-to’ mails which follow a single posting. Again, if you welcome such postings then that’s fine , but reply=sender will prevent those postings at source. By setting reply=sender,respect , this means that, by default, replies will go to the sender, but if the replier wishes to reply to the whole list, they can override this when they compose their message.

So if you still wish to enforce additional security with content filters, then this is how it’s done. Its fairly straightforward, but please note that filters apply only to the text content of the message, any attachments are not examined by the filter and so could still contain the offending material you wish to filter and will be accepted.

If you go to list management and then press the templates button, scroll through the list of templates and select the following:

Rules for filtering list messages based on their contents [CONTENT_FILTER] and then press the Edit Form button.

These templates can have one or more entries, one per line, in the following form

[prefix:] pattern

where prefix is a mail header tag, such as Subject, Header or Text. The default is text and pattern is the character string to search for. This is case insensitive and you can use the * character as a wildcard.

The next line, known as the action rule, is purely optional and be either of the following:

Action:á ALLOW
Action: REJECT reason

The default is REJECT with no reason. If reason is supplied, this is passed to another template, the BAD_CONTENT template, and inserted into theá %COMMENT variable found there. The message in this template is sent to the sender of the message that is blocked by your filter, and like all templates, you can modify this as you wish.

Here are two common examples.

For simple rejection of out of office messages, just in case they slip through our auto-detection mentioned earlier

Text:á out of office
Action: Reject

But since text and reject are the defaults, they aren’t necessary.

To reject postings containing certain words which you find offensive, the simplest way is just to list them, as below


Of course certain words are acceptable in one context but unacceptable or offensive in another, some would say certain words are always offensive. As list owner its your list so you have the final say on what is allowed.

To reject typical spam, which normally allows you to choose not to receive further postings, use the following
áááá Click here to be removed
Action: Reject I do not allow unsolicited mail on áááá my list, please don’t sendá any more

This will send your rejection reason to the poster and of course you are free to use your own words in the reason.





















Text Box: Content Filters   by Les Cesek


JISCmail 2003

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