NAME
slocal - asynchronously filter and deliver new mail
SYNOPSIS
/usr/lib/mh/slocal [address info sender] [-addr address] [-info data]
[-sender sender] [-user username] [-mailbox mbox] [-file file]
[-maildelivery deliveryfile] [-verbose | -noverbose] [-suppressdup
| -nosuppressdup] [-debug] [-version] [-help]
DESCRIPTION
Slocal is a program designed to allow you to have your inbound mail
processed according to a complex set of selection criteria. You do not
normally invoke slocal yourself, rather slocal is invoked on your
behalf by your system’s Message Transfer Agent (such as sendmail) when
the message arrives.
The message selection criteria used by slocal is specified in the file
“.maildelivery” in the user’s home directory. You can specify an
alternate file with the -maildelivery file option. The syntax of this
file is specified below.
The message delivery address and message sender are determined from the
Message Transfer Agent envelope information, if possible. Under
sendmail, the sender will obtained from the UUCP “From:” line, if
present. The user may override these values with command line
arguments, or arguments to the -addr and -sender switches.
The message is normally read from the standard input. The -file switch
sets the name of the file from which the message should be read,
instead of reading stdin. This is useful when debugging a
“.maildelivery” file.
The -user switch tells slocal the name of the user for whom it is
delivering mail. The -mailbox switch tells slocal the name of the
user’s maildrop file.
slocal is able to detect and suppress duplicate messages. To enable
this, use the option -suppressdup. slocal will keep a database
containing the Message-ID’s of incoming messages, in order to detect
duplicates. Depending on your configuration, this database will be in
either ndbm or Berkeley db format.
The -info switch may be used to pass an arbitrary argument to sub-
processes which slocal may invoke on your behalf.
The -verbose switch causes slocal to give information on stdout about
its progress. The -debug switch produces more verbose debugging output
on stderr. These flags are useful when creating and debugging your
“.maildelivery” file, as they allow you to see the decisions and
actions that slocal is taking, as well as check for syntax errors in
your “.maildelivery” file.
Message Transfer Agents
Most modern MTAs including sendmail, postfix and exim support a
.forward file for directing incoming mail. You should include the line
“| /usr/lib/mh/slocal -user username”
in your .forward file in your home directory. This will cause your MTA
to invoke slocal on your behalf when a message arrives.
The Maildelivery File
The “.maildelivery” file controls how slocal filters and delivers
incoming mail. Each line of this file consists of five fields,
separated by white-space or comma. Since double-quotes are honored,
these characters may be included in a single argument by enclosing the
entire argument in double-quotes. A double-quote can be included by
preceding it with a backslash. Lines beginning with ‘#’ and blank
lines are ignored.
The format of each line in the “.maildelivery” file is:
header pattern action result string
header:
The name of a header field (such as To, Cc, or From) that is to
be searched for a pattern. This is any field in the headers of
the message that might be present.
The following special fields are also defined:
source the out-of-band sender information
addr the address that was used to cause delivery to the
recipient
default this matches only if the message hasn’t been delivered
yet
* this always matches
pattern:
The sequence of characters to match in the specified header field.
Matching is case-insensitive, but does not use regular
expressions.
action:
The action to take to deliver the message. When a message is
delivered, a “Delivery-Date: date” header is added which indicates
the date and time that message was delivered.
destroy This action always succeeds. file, mbox, or > Append
the message to the file named by string. The message
is appended to the file in mbox (uucp) format. This
is the format used by most other mail clients (such
as mailx, elm). If the message can be appended to
the file, then this action succeeds.
mmdf Identical to file, but always appends the message
using the MMDF mailbox format.
pipe or | Pipe the message as the standard input to the command
named by string, using the Bourne shell sh to
interpret the string. Prior to giving the string to
the shell, it is expanded with the following built-in
variables:
$(sender) the out-of-band sender information
$(address) the address that was used to cause
delivery to the recipient
$(size) the size of the message in bytes
$(reply-to) either the “Reply-To:” or “From:” field
of the message
$(info) the out-of-band information specified
qpipe or ^ Similar to pipe, but executes the command directly,
after built-in variable expansion, without assistance
from the shell. This action can be used to avoid
quoting special characters which your shell might
interpret.
folder or + Store the message in the nmh folder named by string.
Currently this is handled by piping the message to
the nmh program rcvstore, although this may change in
the future.
result:
Indicates how the action should be performed:
A Perform the action. If the action succeeds, then the message
is considered delivered.
R Perform the action. Regardless of the outcome of the action,
the message is not considered delivered.
? Perform the action only if the message has not been delivered.
If the action succeeds, then the message is considered
delivered.
N Perform the action only if the message has not been delivered
and the previous action succeeded. If this action succeeds,
then the message is considered delivered.
The delivery file is always read completely, so that several
matches can be made and several actions can be taken.
Security of Delivery Files
In order to prevent security problems, the “.maildelivery” file must be
owned either by the user or by root, and must be writable only by the
owner. If this is not the case, the file is not read.
If the “.maildelivery” file cannot be found, or does not perform an
action which delivers the message, then slocal will check for a global
delivery file at /etc/nmh/maildelivery. This file is read according to
the same rules. This file must be owned by the root and must be
writable only by the root.
If a global delivery file cannot be found or does not perform an action
which delivers the message, then standard delivery to the user’s
maildrop is performed.
Example Delivery File
To summarize, here’s an example delivery file:
#
# .maildelivery file for nmh’s slocal
#
# Blank lines and lines beginning with a ’#’ are ignored
#
# FIELD PATTERN ACTION RESULT STRING
#
# File mail with foobar in the “To:” line into file foobar.log
To foobar file A foobar.log
# Pipe messages from coleman to the program message-archive
From coleman pipe A /bin/message-archive
# Anything to the “nmh-workers” mailing list is put in
# its own folder, if not filed already
To nmh-workers folder ? nmh-workers
# Anything with Unix in the subject is put into
# the file unix-mail
Subject unix file A unix-mail
# I don’t want to read mail from Steve, so destroy it
From steve destroy A -
# Put anything not matched yet into mailbox
default - file ? mailbox
# always run rcvtty
* - pipe R /usr/lib/mh/rcvtty
Sub-process environment
When a process is invoked, its environment is: the user/group-ids are
set to recipient’s ids; the working directory is the recipient’s home
directory; the umask is 0077; the process has no /dev/tty; the standard
input is set to the message; the standard output and diagnostic output
are set to /dev/null; all other file-descriptors are closed; the
environment variables $USER, $HOME, $SHELL are set appropriately, and
no other environment variables exist.
The process is given a certain amount of time to execute. If the
process does not exit within this limit, the process will be terminated
with extreme prejudice. The amount of time is calculated as ((size /
60) + 300) seconds, where size is the number of bytes in the message
(with 30 minutes the maximum time allowed).
The exit status of the process is consulted in determining the success
of the action. An exit status of zero means that the action succeeded.
Any other exit status (or abnormal termination) means that the action
failed.
In order to avoid any time limitations, you might implement a process
that began by fork()-ing. The parent would return the appropriate
value immediately, and the child could continue on, doing whatever it
wanted for as long as it wanted. This approach is somewhat risky if
the parent is going to return an exit status of zero. If the parent is
going to return a non-zero exit status, then this approach can lead to
quicker delivery into your maildrop.
FILES
/etc/nmh/mts.conf nmh mts configuration file
$HOME/.maildelivery The file controlling local delivery
/etc/nmh/maildelivery Rather than the standard file
/var/mail/$USER The default maildrop
SEE ALSO
rcvdist(1), rcvpack(1), rcvstore(1), rcvtty(1), mh-format(5)
DEFAULTS
‘-noverbose’
‘-nosuppressdup’
‘-maildelivery’ defaults to $HOME/.maildelivery
‘-mailbox’ deaults to /var/mail/$USER
‘-file’ defaults to stdin
‘-user’ defaults to the current user
CONTEXT
None
HISTORY
Slocal was originally designed to be backward-compatible with the
maildelivery facility provided by MMDF-II. Thus, the “.maildelivery”
file syntax is somewhat limited. But slocal has been modified and
extended, so that is it no longer compatible with MMDF-II.
In addition to an exit status of zero, the MMDF values RP_MOK (32) and
RP_OK (9) mean that the message has been fully delivered. Any other
non-zero exit status, including abnormal termination, is interpreted as
the MMDF value RP_MECH (200), which means “use an alternate route”
(deliver the message to the maildrop).
BUGS
Only two return codes are meaningful, others should be.
Slocal was originally designed to be backwards-compatible with the
maildelivery functionality provided by MMDF-II.