Apple Mac OS X Server Version 10.4 or Later Manual de usuario descargar pdf (Pagina 50)

50 Chapter 1 Mail Service Setup

Enabling Junk Mail Screening (Baysian Filters)

Before you can benefit from mail screening, it must be enabled. While enabling

screening, you configure certain screening parameters. Bayesian mail filtering is the

classification of mail messages based on statistics. Each message is analyzed and the

word frequency statistics are saved. Mail messages that have more of the same words

as junk mail receive a higher marking of probability that they are also junk mail. When

the message is screened, the server adds a new header (“X-Spam-Level”) with the junk

mail probability score.

For example, let’s say you have 400 mail messages. 200 of them are junk mail, and 200

of them are good mail. When a new message arrives, its text is compared to the 200

junk mail, and the 200 good mail. The the filter assigns it a probability of being junk or

good, depending on what group it most resembles.

Bayesian filtering has shown itself to be a very effective method of finding junk mail, if

the filter has enough data to go on. One of the strengths of this method is the more

mail you get and classify (a process called “training”), the more accurate the next round

of classification is. Even if junk mail senders alter their mailings, the filter takes that into

account the next time around.

To enable junk mail screening:

1 In Server Admin, select Mail in the Computers & Services pane.

2 Click Settings.

3 Select the Filters tab.

4 Select Scan Email for Junk Mail.

5 Set the level of permissiveness (Least, Moderate, Most).

The permissiveness meter sets how many junk mail flags can be applied to a single

message before it processed as junk mail. If you set it as “Least permissive,” any mildly

suspicious email will be tagged and processed as junk mail. If you set it for “Most

permissive” it will take a high score (in other words, a lot of junk mail characteristics) to

mark it as junk.

6 Decide how to deal with junk mail messages.

Bounced: Will send the message back to the sender. You can optionally send an

email notification of the bounce to some email account, probably the postmaster.

Deleted: Will delete the message without delivery. You can optionally send an email

notification of the bounce to some email account, probably the postmaster.

Delivered: Will deliver the message in spite of probably being junk mail. You can

optionally add text to the subject line, indicating that the message is probably junk

mail, or encapsulate the junk mail as a MIME attachment.

Redirected: Will deliver the message to someone other than the intended recipient.

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Apple Mac OS X Server Version 10.4 or Later Manual de usuario Pagina 50