Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

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

Sendmail

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directive lets you name such a file, conventionally /etc/mail/domains (not to be

confused with /etc/mail/domaintable).

FEATURE(`masquerade_entire_domain')dnl

The feature masquerade_entire_domain causes MASQUERADE_DOMAIN to be inter-

preted as an entire domain rather than a hostname.

FEATURE(`masquerade_envelope')dnl

This feature causes sender addresses to be masqueraded not only in the From:

header field but also in the SMTP envelope.

EXPOSED_USER(username)dnl

EXPOSED_USER

specifies a username for whom the From address should not be

masqueraded. root is a popular candidate for this, since email from root often

contains alerts and warnings; if you receive such an alert or warning, you gener-

ally want to know which host sent it.

These are the most important sendmail.mc settings for security purposes. There are

many other nonsecurity settings, however. For more information, see the README.cf

or cf.README.gz file I alluded to earlier in this section.

Applying your new configuration

To compile your macro-configuration file into sendmail.cf, use this command:

bash-# m4 /etc/mail/sendmail.mc > /etc/sendmail.cf

If your macro-configuration file’s name isn’t sendmail.mc, substitute it with linux.mc

or whatever yours is called. Sendmail expects its configuration file to be named send-

mail.cf ...