Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 9: Securing Internet Email

useful sometimes to write certain types of messages to a text file rather than to a

mailbox.)

One caveat: if an alias points to a different mail server, that server

must belong to a domain for which the SMTP gateway is configured to

relay mail (i.e., either that server’s FQDN or its domain must be listed

in the

relay_domains declaration in main.cf).

Don’t forget to run postalias /etc/aliases any time you edit aliases. postalias con-

verts the alias file into a database file that can be searched repeatedly and rapidly

each time a destination address is parsed; neither Postfix nor Sendmail directly use

the text version of aliases.

Keeping Out Unsolicited Commercial Email (UCE)

Postfix offers protection against UCE via several settings in main.cf. Some caution is

in order, however: there’s a fine line between spam and legitimate dissemination,

and it’s entirely possible that even modest UCE controls will cause some legitimate

(i.e., desired) mail to be dropped.

Having said that, for most sites, this is an acceptable risk (avoidable, too, through

end-user education), and we recommend that at a minimum you set the following in

main.cf (for a complete list of anti-UCE parameters and their exact syntax, see /etc/

postfix/sample-smtpd.cf):

smtpd_recipient_limit ...