Apple Mac OS X Server Version 10.4 or Later Manual do Utilizador descarregar pdf (Página 46)

46 Chapter 1 Mail Service Setup

Limiting Junk Mail and Viruses

You can configure your mail service to decrease the volume of unsolicited commercial

mail, also known as junk mail (or spam), and email containing viruses. You can take

steps to block junk mail or viruses that are sent to your mail users. Additionally, you can

secure your server against use by mail service abusers, who try to use your resources to

send junk mail to others.

You can also take steps to prevent senders of junk mail from using your server as a

relay point. A relay point or open relay is a server that unselectively receives and

forwards all mail addressed to other servers. An open relay sends mail from any domain

to any domain. Junk mail senders exploit open relay servers to avoid having their own

SMTP servers blacklisted as sources of junk mail. You don’t want your server blacklisted

as an open relay, because other servers may reject mail from your users.

There are two main methods of prevent viruses and junk mail passing through or into

your mail system. Using both of the methods in concert will help ensure your mail

system integrity. The two points of control are:

• “Connection Control” (next).

• “Email Screening” on page 49.

Connection Control

This method of prevention controls which servers can connect to your mail system, and

what those servers have to do to send mail through your mail system. Your mail service

can do any of the following to exercise connection control:

• Require SMTP authentication

• Restrict SMTP relay, allowing relay only by approved servers

• Reject all SMTP connections from disapproved servers

• Reject mail from blacklisted servers

• Filter SMTP connections

Requiring SMTP Authentication

If your mail service requires SMTP authentication, your server cannot be used as an

open relay by anonymous users. Someone who wants to use your server as a relay

point must first provide the name and password of a user account on your server.

Although SMTP authentication applies primarily to mail relay, your local mail users

must also authenticate before sending mail. This means your mail users must have mail

client software that supports SMTP authentication or they will be unable to send mail

to remote servers. Mail sent from external mail servers and addressed to local recipients

will still be accepted and delivered.

To require SMTP authentication, please see “Enabling Secure SMTP Authentication” on

page 33, and “Enabling Less Secure SMTP Authentication” on page 34.

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Apple Mac OS X Server Version 10.4 or Later Manual do Utilizador Página 46