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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define(`confSMTP_LOGIN_MSG', `message')dnl

This variable defines the banner string that sendmail sends to remote clients at

the beginning of each SMTP session. By default, this string is set to:

`$j Sendmail $v/$Z; $b'

where $j expands to the local Fully Qualified Domain Name (FQDN), $v

expands to the sendmail daemon’s version, $Z expands to the version number of

the m4 configuration, and

$b expands to a time/date stamp.

In truth, none of this information needs to be provided. I personally prefer to set

my Sendmail login message to a minimal

`Sendmail'.

define(`confSAFE_FILE_ENV', `/path/to/jail')dnl

This definition tells Sendmail to set sendmail.cf’s SafeFileEnvironment variable to

some subdirectory of / to which sendmail will chroot when writing files. For

more information, see the section entitled “Configuring Sendmail to Run Semi-

chrooted.”

define(`confUNSAFE_GROUP_WRITES')dnl

In Example 9-1, confUNSAFE_GROUP_WRITES has been set to true.Iftrue,

confUNSAFE_GROUP_WRITES causes Sendmail to log a warning message whenever

mail is handled by a .forward or :include: file that is group- or world-writable.

Furthermore, if such a .forward or :include: file contains any address pointing to

an unsafe file, such as an executable, the message being processed will be

bounced and logged ...