MIMEDEFANG(8) System Manager's Manual MIMEDEFANG(8)
NAME
mimedefang - Sendmail MIME mail filter
SYNOPSIS
mimedefang prcap
mimedefang -p connection -m mx_socket_name -U user [options]
DESCRIPTION
mimedefang is a filter built around Sendmail 8.11's milter API for mail filters. It collects each incoming message and runs a filter on
the message. This is useful for deleting attachments which may be a security risk on poorly-designed systems like Microsoft Windows.
mimedefang does not actually run the Perl filter; instead, it communicates with mimedefang-multiplexor(8), which manages a pool of persis-
tent Perl processes. See the mimedefang-multiplexor man page for additional information.
OPTIONS
If you invoke mimedefang with the single argument prcap, it prints information about the version of Milter it is linked against and exits.
Otherwise, you should invoke mimedefang as shown in the second line of the SYNOPSIS.
-U user
Runs mimedefang as user rather than root. The user argument must match the argument to mimedefang-multiplexor's -U option as well.
-z spooldir
Set the spool directory to spooldir. If this option is omitted, the spool directory defaults to /var/spool/MIMEDefang.
-p connection
The -p switch is required and specifies the milter connection type. Typically, you should run mimedefang on the same computer as
sendmail. Therefore, you should use a UNIX-domain socket for the connection type. The suggested value for the -p switch is mimede-
fang.sock under the spool directory.
-m mx_socket_name
Specifies the socket for communicating with mimedefang-multiplexor(8). The mx_socket_name specifies the path of the UNIX-domain
socket. See mimedefang-multiplexor(8) for details.
-b backlog
Sets the "backlog" argument to the listen(2) system call to backlog. If this option is omitted, then the operating-system default
backlog is used.
-d The -d switch causes mimedefang not to delete the temporary spool files it creates for incoming messages. This is for debugging
purposes only and should never be used on a production mail server.
-r Causes mimedefang to perform a relay check before processing any messages. It calls into a user-supplied Perl function called fil-
ter_relay with the IP address and host name of the sending relay. (See mimedefang-filter(5) for details.)
-H Causes mimedefang to perform a HELO check before processing any messages. It calls into a user-supplied Perl function called fil-
ter_helo with the IP address and host name of the sending relay, and the HELO argument. (See mimedefang-filter(5) for details.)
-s Causes mimedefang to perform a sender check before processing the message body. It calls into a user-supplied Perl function called
filter_sender with the envelope address of the sender. (See mimedefang-filter(5) for details.)
-t Causes mimedefang to perform recipient checks before processing the message body. It calls into a user-supplied Perl function
called filter_recipient with the envelope address of each recipient. (See mimedefang-filter(5) for details.)
-q Permits the multiplexor to queue new connections. See the section QUEUEING REQUESTS in the mimedefang-multiplexor man page. Note
that this option and the -R option are mutually-exclusive. If you supply -q, then -R is ignored.
-k Causes mimedefang not to delete working directories if a filter fails. This lets you obtain the message which caused the filter to
fail and determine what went wrong. mimedefang logs the directory containing the failed message using syslog.
-P fileName
Causes mimedefang to write its process-ID (after becoming a daemon) to the specified file.
-R num Normally, mimedefang tempfails a new SMTP connection if there are no free slaves. Supplying the -R num option makes mimedefang
tempfail new connections if there are fewer than num free slaves, unless the connection is from the local host. This allows you to
favour connections from localhost so your clientmqueue doesn't build up. Note that supplying -R 0 is subtly different from omitting
the option; in this case, mimedefang permits new connections from localhost to queue, but not connections from other hosts (unless
you also supply the -q option.)
The purpose of the -R option is to reserve resources for clientmqueue runs. Otherwise, on a very busy mail server, clientmqueue
runs can starve for a long time, leading to delays for locally-generated or streamed mail. We recommend using a small number for
num; probably no more than 3 or 10% of the total number of slaves (whichever is smaller.)
Note that this option and the -q option are mutually-exclusive. If you supply -q, then -R is ignored.
-C Conserve file descriptors by opening and closing disk files more often. (Disk files are never held open across Milter callbacks.)
While this shortens the length of time a file descriptor is open, it also leaves more opportunities for the open to fail. We do not
recommend the use of this flag except on very busy systems that exhibit failures due to a shortage of file descriptors.
-T Causes mimedefang to log the run-time of the Perl filter using syslog.
-x string
Add string as the content of the X-Scanned-By: header. If you set string to the empty string (i.e. -x ""), then no X-Scanned-By:
header will be added.
-X Do not add an X-Scanned-By: header. Specifying -X is equivalent to specifying -x "".
-D Do not fork into the background and become a daemon. Instead, stay in the foreground. Useful mainly for debugging or if you have a
supervisory process managing mimedefang.
-M This option is obsolete; it is accepted for backward-compatibility, but is ignored.
-N Normally, mimedefang sees all envelope recipients, even ones that Sendmail knows to be invalid. If you don't want Sendmail to per-
form a milter callback for recipients it knows to be invalid, invoke mimedefang with the -N flag. Please note that this flag only
works with Sendmail and Milter 8.14.0 and newer. It has no effect if you're running an older version of Sendmail or Milter.
-S facility
Specifies the syslog facility for log messages. The default is mail. See openlog(3) for a list of valid facilities. You can use
either the short name ("mail") or long name ("LOG_MAIL") for the facility name.
-a macro
Pass the value of the specified Sendmail macro through to the Perl filter. You can repeat the -a option to write more macros than
the built-in defaults. Note that in addition to asking mimedefang to pass the macro value to the filter, you must configure Send-
mail to pass the macro through to mimedefang using the confMILTER_MACROS_ENVFROM definition in Sendmail's m4 configuration file.
-c Strip "bare" carriage-returns (CR) characters from the message body. A bare CR should never appear in an e-mail message. Older
versions of mimedefang used to strip them out automatically, but now they are left in by default. The -c option enables the older
behavior.
-h Print usage information and exit.
OPERATION
When mimedefang starts, it connects to sendmail using the milter API. (See the Sendmail 8.11 documentation.) For each incoming message,
mimedefang creates a temporary directory and saves information in the directory. At various phases during the SMTP conversation, mimede-
fang communicates with mimedefang-multiplexor to perform various operations. mimedefang-multiplexor manages a pool of persistent Perl pro-
cesses that actually perform the mail scanning operations.
When a Perl process scans an e-mail, the temporary spool directory contains certain files; details of the communication protocol between
mimedefang and the Perl script are in mimedefang-protocol(7).
WARNINGS
mimedefang does violence to the flow of e-mail. The Perl filter is quite picky and assumes that MIME e-mail messages are well-formed.
While I have tried to make the script safe, I take no responsibility for lost or mangled e-mail messages or any security holes this script
may introduce.
AUTHOR
mimedefang was written by David F. Skoll <dfs@roaringpenguin.com>. The mimedefang home page is http://www.mimedefang.org/.
SEE ALSO
mimedefang.pl(8), mimedefang-filter(5), mimedefang-multiplexor(8), mimedefang-protocol(7)
4th Berkeley Distribution 8 February 2005 MIMEDEFANG(8)