04-24-2011
I am an older administrator who still uses Sendmail. I have about 20 years experience with it and I can solve any Sendmail problem I encounter. It was a nasty learning curve and I really don't want to do that again. Sendmail has had more than its share of problems over the years but now it seems pretty stable. It would be possible to switch to postfix but I don't see any reason to do that. Exchange is not even a possible option as far as I know... it doesn't run on Unix. Postfix is the only alternative I know... are there other MTA's available for Unix?
I have to say we Sendmail users probably should not chide Exchange on its security problems though.... people who live in glass houses shouldn't be throwing stones.
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SMRSH(8) System Manager's Manual SMRSH(8)
NAME
smrsh - restricted shell for sendmail
SYNOPSIS
smrsh -c command
DESCRIPTION
The smrsh program is intended as a replacement for sh for use in the ``prog'' mailer in sendmail(8) configuration files. It sharply limits
the commands that can be run using the ``|program'' syntax of sendmail in order to improve the over all security of your system. Briefly,
even if a ``bad guy'' can get sendmail to run a program without going through an alias or forward file, smrsh limits the set of programs
that he or she can execute.
Briefly, smrsh limits programs to be in a single directory, by default /usr/lib/sendmail.d/bin/ allowing the system administrator to choose
the set of acceptable commands, and to the shell builtin commands ``exec'', ``exit'', and ``echo''. It also rejects any commands with the
characters ``', `<', `>', `;', `$', `(', `)', `
' (carriage return), or `
' (newline) on the command line to prevent ``end run'' attacks.
It allows ``||'' and ``&&'' to enable commands like: ``"|exec /usr/local/bin/filter || exit 75"''
Initial pathnames on programs are stripped, so forwarding to ``/usr/bin/vacation'', ``/usr/bin/vacation'', ``/home/server/mydir/bin/vaca-
tion'', and ``vacation'' all actually forward to `/usr/lib/sendmail.d/bin/vacation''.
System administrators should be conservative about populating the /usr/lib/sendmail.d/bin/ directory. For example, a reasonable additions
is vacation(1), and the like. No matter how brow-beaten you may be, never include any shell or shell-like program (such as perl(1)) in the
/usr/lib/sendmail.d/bin/ directory. Note that this does not restrict the use of shell or perl scripts in the /usr/lib/sendmail.d/bin/
directory (using the ``#!'' syntax); it simply disallows execution of arbitrary programs. Also, including mail filtering programs such as
procmail(1) is a very bad idea. procmail(1) allows users to run arbitrary programs in their procmailrc(5).
COMPILATION
Compilation should be trivial on most systems. You may need to use -DSMRSH_PATH="path" to adjust the default search path (defaults to
``/bin:/usr/bin'') and/or -DSMRSH_CMDDIR="dir" to change the default program directory (defaults to ``/usr/lib/sendmail.d/bin/'').
FILES
/usr/lib/sendmail.d/bin/ - default directory for restricted programs on SuSE Linux
SEE ALSO
sendmail(8)
$Date: 2004/08/06 03:55:35 $ SMRSH(8)