In this section, we discuss the most common security features:
??? Th eT configuration command (class t) defines which users are allowed to use
the -f command-line switch to override the sender address with one of their
own, and which users are allowed to rebuild the aliases database.
??? Th esmrsh program replaces /bin/sh as the program run by the prog delivery
agent to execute programs. The smrsh program is simple yet immensely valuable.
We recommend that it be routinely installed on all your machines. The
smrsh program is described in detail in ?§10.8 on page 379.
??? Several options can be used to tighten security and to provide reports of security
violations.
??? Th e/etc/shells file prevents ordinary users from running programs on your mail
server.
4.8.1 Trusted Users
Under pre-V8 sendmail, trusted users are those who are allowed to use the -f
command-line switch(?§6.7.24 on page 241) to override the sender address withone
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174 | Chapter 4: Maintain Security with sendmail
of their own. V8.1 sendmail eliminated this configuration command. V8.7 restored it,
but as a class, and uses that class only to suppress warning headers. V8.11 and above
allow only users in that class to rebuild the aliases database.
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