Ubuntu Manpage: mimedefang - Sendmail MIME mail filter

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 persistent 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.

-y If the -y command-line option is given, MIMEDefang will call smfi_setsymlist to set
the list of macros it wants. This function leaked memory in versions of Sendmail
prior to 8.14.4 so by default we do not call it. If you are running an older
version of sendmail, you should explicitly set the list of macros you want in the
Sendmail configuration file.

-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 mimedefang.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.

-G Normally, mimedefang uses a umask of 077 when creating the milter socket and files.
If you would like the socket to be readable and writeable by the group and files to
be group-readable, supply the -G option. This causes the umask to be 007 whenever
UNIX-domain sockets are created and 027 whenever files are created. Note: if your
milter library is too old to have the smfi_opensocket() function, the -G option
causes mimedefang to use a umask of 007 throughout its execution.

Note that by default, /var/spool/MIMEDefang is created with mode 0700. If you use
the -G option, you probably should change the mode to 0750.

-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 filter_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 filter_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. The file will be owned by root.

-o fileName
Causes mimedefang to use fileName as a lock file to avoid multiple instances from
running. If you supply -P but not -o, then mimedefang constructs a lock file by
appending ".lock" to the pid file. However, this is less secure than having a
root-owned pid file in a root-owned directory and a lock file writable by the user
named by the -U option. (The lock file must be writable by the -U user.)

-R num Normally, mimedefang tempfails a new SMTP connection if there are no free workers.
Supplying the -R num option makes mimedefang tempfail new connections if there are
fewer than num free workers, 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
workers (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 perform 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 Sendmail 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,
       mimedefang   communicates  with  mimedefang-multiplexor  to  perform  various  operations.
       mimedefang-multiplexor manages a pool of persistent Perl processes 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 Dianne Skoll <dfs@roaringpenguin.com>.  The mimedefang home page
       is http://www.mimedefang.org/.