mimedefang (8) - Linux Manuals
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.
- -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 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).