Provided by: nmh_1.8-3_amd64 
NAME
slocal - asynchronously filter and deliver new mail to nmh
SYNOPSIS
/usr/lib/mh/slocal [-help] [-version] [-addr address] [-info data] [-sender sender] [-user username]
[-mailbox mbox] [-file file] [-maildelivery deliveryfile] [-verbose | -noverbose] [-suppressdup |
-nosuppressdup] [-debug]
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 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. It must exist on the
local system. The -mailbox switch tells slocal the name of the user's mail drop 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 whitespace 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 by piping the message to the nmh program
rcvstore.
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 root and must be writable only by 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 mail drop 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 mail drop.
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 mail drop
SEE ALSO
rcvdist(1), rcvpack(1), rcvstore(1), rcvtty(1), mh-format(5)
DEFAULTS
`-noverbose'
`-nosuppressdup'
`-maildelivery' defaults to $HOME/.maildelivery
`-mailbox' defaults to /var/mail/$USER
`-file' defaults to stdin
`-addr' defaults to the current user
`-user' defaults to the current user
-addr and -user will be set the the user part of the Local-Mailbox profile entry, if set.
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 mail
drop).
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.
nmh-1.8 2022-03-13 SLOCAL(1mh)