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/.