sortmail - Online in the Cloud

PROGRAM:

NAME

sortmail - classify incoming mail

SYNOPSIS

sortmail [ -v ] [ -terse ] [ -home path ] [ -mailbox path ] [ -mailrc initfile ] [
-sortmailrc initfile ] [ -inbox filename ] [ -mbox ] [ -pop|pop3|pop2 user:password@host ]
[ -pop|pop3|pop2 /path ] [ -keep ] [ -noapop ] [ var=value ] [ -dumpCrcs dbmname ] [
-verify ] [ -version ] username

DESCRIPTION

Sortmail reads and classifies email according to patterns you specify. It can be used to
process incoming mail, filter mailing lists, process mail folders or download mail from
POP servers.

For processing incoming mail, create this .forward file in your home directory:

"| /path/sortmail user"

Where "/path/sortmail" is the full path where you installed sortmail, and user is your own
userid. The userid must be specified because when mail arrives, sortmail could be run as
root, daemon, or any number of other uid's.

Once your .forward file is set up, sortmail will classify incoming mail according to the
patterns in $HOME/.sortmailrc. Your .sortmailrc file is similar to a news KILL file, but
somewhat more powerful. You can discard mail, have it delivered to your mailbox, have it
filed into a folder, forward it to another address or even pipe it through a shell
command.

Don't let the long list of options and command below frighten you. New users might do
well to skip to the EXAMPLES section below, and/or read the README and sample files in
/usr/share/doc/sortmail.

When sortmail starts up, it first reads the following config files: /usr/lib/sortmailrc,
/usr/local/lib/sortmailrc, /etc/sortmailrc, /usr/etc/sortmailrc,
/usr/local/etc/sortmailrc, $HOME/.mailrc and $HOME/.sortmailrc.

OPTIONS

-v Verbose. A message is printed stderr or a log file of your choosing for
every mail message. A second -v causes a lot more information to be
printed.

-terse Set verbosity to 1, omit timestamps.

-home path Set user's home directory, overriding the default taken from the user's
passwd entry.

-mailbox path Set the user's system mailbox, overriding the default for your system
(/var/mail/user).

-mailrc path Set the .mailrc file, overriding the default of ~/.mailrc. Path may be
specified as /fullpath, ~/path, ~user/path, or path. The last form is the
same as ~/path.

-sortmailrc path
Set the .sortmailrc file, overriding the default of ~/.sortmailrc. Path
may be specified as with -mailrc, above.

-inbox filename
Take input from named file instead of stdin. Filename may be /abspath
"~/path", "~user/path" or "+foldername". When POP2 protocol is used, this
option can be used to select the inbox instead of the default mailbox.

-mbox Indicates that input is a standard Berkeley mailbox containing multiple
messages, rather than a single message. Used to process an entire mailbox
at once.

-pop user:password@host
Sortmail connects to the specified server, downloads mail and processes it.
If password is not specified, the user is prompted interactively. Note: it
is highly recommended that you do not specify the password on the command
line on a multi-user system, see below.

Sortmail attempts to use pop3 and pop2 protocols in that order. For
obvious reasons, the user id may not contain ':'.

Many providers assign usernames that contain '@', e.g. [email protected]. In
this case, the argument to -pop will look something like
[email protected]@pop.foo.com.

For security reasons, sortmail attempts to hide this information from the
"ps" command, but this does not work under all operating systems (e.g.
Solaris). It is strongly discouraged to specify the password on the
command line for this reason.

-pop /path This variant of the -pop command reads a single line from the specified
file, containing user:password@host. This is more secure than specifying
the password on the command line. File must be specified as a full
pathname, starting with '/'.

-pop3 user:password@host

-pop3 /path Sortmail connects to the specified pop3 server, downloads mail and
processes it.

-pop2 user:password@host

-pop2 /path Sortmail connects to the specified pop2 server, downloads mail and
processes it.

-keep For POP use or when -inbox and -mbox are specified. Indicates that all
messages are to be left in the source input box instead of being deleted.

-noapop For POP3, do not attempt to use APOP authentication. This option is used
when dealing with broken servers which do not handle APOP correctly.

variable=value Set a variable on the command line. Spaces are not permitted in the
string.

-dumpCrcs dbmname
Dump the bounce-check database in dbmname.{dir,pag} for debugging purposes.

-verify Verify only. Examine the mailrc and sortmailrc files for errors and exit.

-version Print version and exit. If this option fails, you have version
1.something.

SORTMAILRC FORMAT

Your .sortmailrc file is a series of lines in the form

set variable=value

/regular-expression/modifiers:command[:command...]

[ip-address]modifiers:commands..

[ip-address/mask]modifiers:commands..

[ip-address - ip-address]modifiers:commands..

(logical-expression):command[:command...]

includerc filename

listinclude filename

listexclude filename

header headerline

replace headerline

bouncecheck dbmname

where regular-expression is any ed(1)-style regular expression, modifier is any of i, t,
f, s, h, a, o, and command is one of m, j, v, f file, a file, d file, +file, or | command.
Multiple commands may be placed on a line, separated by ':'s. If you need to place a ':'
within a command for any reason, escape it with '\'.

Users of rn-style KILLfiles will be familiar with this format.

The [ip-address] form specifies a literal IP address to be matched (e.g. 192.168.3.4) or a
partial IP address (e.g. 192.168.3). This differs from a regular expression in that the
'.' character must match literally, and the pattern must match at the start (e.g.
129.192.168.3 would not match the pattern given above.) (Note that the '[]' characters
are literal here, and do not denote an optional argument.)

IP addresses may also be specified as a range, e.g. "[192.168.0.0/16]" would match all IP
addresses containing 192.168 in the first 16 bits. Finally, IP addresses may also be
specified as e.g. "[192.168.0.0 - "192.168.255.255]".

SEARCH MODIFIERS

These modifiers affect how the regular expression is applied to the incoming mail. The
default is 's'.

i Ignore case.

o Evaluate variables in pattern only once, when sortmailrc file is read. Without this
option, variables are evaluated every time the pattern is tested. If the pattern
contains no variables, this modifier has no effect.

s Test the "Subject: " line of the mail against the regular expression.

t Test the "To: ", "Cc: " and "Apparently-To: " lines of the mail against the regular
expression.

f Test the "From: " line of the mail against the regular expression.

r Test the Received: lines of the incoming mail against the regular expression.

h Test the entire header of the incoming mail against the regular expression.

a Test the entire incoming mail message against the regular expression.

Any combination of s,t,f,h,a may be used. If none are specified, 's' is assumed.

SEARCH COMMANDS

These commands are executed for any message which matches a search pattern.

:m Send the message to the user's mailbox.

:m address
Forward the mail to the specified address.

:j Delete the message ("junk" it.)

:e n Set the exit code to n. When processing is complete, sortmail will exit with
the given exit code instead of zero.

:E n Exit immediately with exit code n.

:k Keep the message. When downloading messages from a POP server, or when -inbox
and -mbox are specified, messages are normally deleted from the mailbox once
transfer is successful. This option causes the message to be left behind.

:f folder Append the message to the given mail folder. folder may be in the formats
~/path, /abspath, ~user/path, or +name. The latter form expands to
~/folder/name where folder is the value specified for the $folder variable
(default is "folders".)

:+folder Shorthand for "f +folder".

:d file Append the message to the given file in digest form. file may be in the formats
~/path, /abspath, ~user/path, or +name.

"Digest" form is a stripped form where each message contains only the "From:",
"Subject:" and "Date:" headers, and messages are separated by a line of dashes.

:a file "Archive". Identical to digest.

:| command
Pipe the mail message through the given shell-command. sh(1) is used.

:c Continue processing. Normally, sortmail applies search expressions to mail
messages until a match is found. At this point, the message is dispatched and
sortmail is finished. This command causes sortmail to continue comparing the
message to more patterns. This option may be considered "continue", "Cc" or
"copy" at your whim. Thus, a message may be sent to more than one destination.

COMMANDS

The following is a list of commands which may be contained within a .mailrc or .sortmailrc
file.

set variable = value
Set an environment variable. Variables used by sortmail are listed below. Quotes
around the string are not needed. Special characters such as '$' or '\' may be
quoted with '\'. Variables may be included within the value string in the form
$name or ${name}.

Note that the set command is processed immediately when the initfile is read. Other
commands are processed as mail messages are read. Thus, all set commands are
processed before any other commands, regardless of their order in the init files.

listinclude filename
Used for mailing list administration (see below). Ignore this command if you're not
using sortmail to administer a mailing list.

This command specifies a file containing a list of addresses which are permitted to
post to the list. Each line of the file contains one regular expression, which
represents the email address of a list member. Lines in the format

User Name <address>

will only use the address part of the line. This allows the mailing list itself to
be used as the include list.

Multiple include lists may be specified with multiple listinclude commands. If the
listinclude command is used, posters to the list must be found in at least one of
the lists. If no include files are specified, anybody may post.

Messages which are rejected are handled according to the $reject variable, which
must exist and which contains either a filename or a search command (see below.)

For more on include and exclude files, see MAILING LISTS, below.

listexclude filename
Specify a list of addresses which are not permitted to post to the list. Same
format as listinclude. In order to post to the list, a user must be in the
listinclude file(s) (if any) and not in the listexclude file(s).

replace Header: value
Used for mailing list processing. Headers lines matching the specified header are
replaced with the new value. If no match is found, the line is appended to the
message header. Typically used to change the "From: " header to specify the list
address rather than the originator, and to set an "Errors-To: " header.

If the value field is empty, the specified header line is deleted.

header Header: value
Same format as replace, except that header lines are always appended to the header,
not replaced. Typically used to add comments.

bouncecheck dbmname
Last resort mechanism for detecting mail loops. A crc-32 hash of the text portion
of the message is computed and stored in dbmname.{dir,pag}. If another message with
the same hash code is encountered in the next 60 days, the message is rejected and
disposed of as described in $reject

This is not a perfect mechanism, however, as broken mailers may choose to add some
comments to the message before bouncing it back.

includerc filename
Process commands from named file. Include files may be nested.

VARIABLES

Variables are used in the form $name or ${name}. Variables may appear anywhere in the
init file.

Sortmail uses the following variables, which may be changed in your .mailrc or .sortmailrc
files. Variables may also be set on the command line.

default Command(s) used to handle unclassifiable mail. The default behavior is to put
unclassifiable mail into mailbox. Another reasonable value might be "+other".

delay Used to prevent runaway mail loops; especially useful for mailing list
administration. Specifies a delay in seconds to be imposed before mail is
forwarded to another address or piped through a command. For example, a
600-second delay (ten minutes) would limit a mail loop to one message every ten
minutes.

folder The user's mail folders directory. Mail folders are denoted by a leading '+' in
their name, and are stored in ~user/$folder/. Default is "folders". Many
people choose to set this to "Mail" instead.

from Used for mailing list administration. Specifies the value of the "From " line
when mail is forwarded to the list. Not all versions of sendmail will honor
this. You may need to make sortmail suid-uucp or add your username to the
"trusted users" entry in /etc/sendmail.cf.

HOME The user's home directory. Used to find initialization files and the user's
folders directory. Default is ~user.

lines Count of lines of text in the message. Set by sortmail and updated for every
message.

logfile Debugging messages are sent to the specified log file. If sortmail is executed
from the command line, the default is stderr. Otherwise the default is
/tmp/sortmail.log.

If logfile cannot be opened, stderr is used. Note that when sortmail is used
from your .forward file to filter incoming messages, messages sent to stderr
will be sent back to the sender as bounces.

mailbox The user's mail box. Default is /var/mail/user.

mailrc Full path of the user's .mailrc file. There's no real point in changing this.

maxlines Maximum number of message lines which will be searched during pattern matching.
Restricting this value can make searches quicker and prevent the /tmp directory
from filling. Default value is 5000.

reject Used for mailing list administration. Specifies the file or command to which
rejected mail is sent.

sendmail The command used to deliver mail. Default value is "/usr/lib/sendmail -om -oi".
If '%f' occurs in the string, it will be expanded to the temporary file name
containing the message. Otherwise, the message will be delivered to the
command's standard input.

Special values "SMTP" and "SMTP hostname" cause the message to be delivered
directly to an SMTP port.

size Size of message in bytes. Set by sortmail and updated for every message.

sortmailrc
Full path of the user's .sortmailrc file. There's no real point in changing
this.

timeout Timeout in seconds for POP connections.

user The user on behalf of whom sortmail is running. This value must be specified on
the command line when sortmail is executed from a .forward file, but may be
changed later. It is used to determine the user's home directory, among other
things.

vacation If set, mail to user will also be piped through vacation(1).

TMPDIR Directory used for temporary files. Default is "/tmp".

In addition, sortmail defines the following environment variables before passing a message
to another program.

FROM The sender of the message

SUBJECT The subject line from the incoming message

EXAMPLES

Here is a sample .sortmailrc file:

set default=+other
/MAILER-DAEMON/f:+bounces
/falk/t:m
/bldg8/t:m
/joe/f:m:c
/for brenda/s:k
/scubaclub/t:+scuba
/scuba/s:+scuba
/marko/f:j
/testing/t:m falk@lab
/jym@apple/f:| /home/falk/bin/fixjim
/^Precedence: junk/h:+other
(/bill/f && /dive/s):+scuba
[211.114.0.0/16]r:j

In this example, the folder directory and other variables have whatever values were
specified in .mailrc. Unclassifiable mail will be sent to the folder "+other". Mail from
"MAILER-DAEMON" is sent to the folder "+bounces". Mail to "falk" or "bldg8" is sent
directly to my mailbox.

Mail from my friend joe is sent directly to my mailbox, and processing continues in order
to see if there's somewhere else it should go as well.

Mail labeled "for brenda" is left at the POP server untouched. (This only works if the
email is being downloaded from a POP server; it would be lost otherwise.)

Mail to the scuba club or with "scuba" in the subject line is sent to the "+scuba" folder.
Mail from marko is thrown away unread. Mail to the "testing" alias is forwarded to my
account on another machine.

Mail from my friend jym, who formats his mail in a funny way is passed through a shell
script which cleans up his messages and appends them to my mailbox. Mail messages with
"^Precedence: junk" anywhere in the header are filed in +other.

The next-to-last line shows a feature new to sortmail version 2: logical expressions. In
this case, mail from bill with the subject "dive" is added to the scuba folder. Logical
expressions are described in detail below.

Finally, the last line shows another feature new to sortmail version 2: IP ranges. In
this case, all email with an IP address in the "211.114.0.0/16" range in a "Received:"
line will be junked unread.

Note that the patterns are applied in the order given; it is important, for example, that
the "MAILER-DAEMON" pattern precede the "falk" pattern so that mail from MAILER-DAEMON is
filed in +bounces even if directed to me personally. Similarly, mail from marko will not
be junked if addressed to me personally.

LOGICAL EXPRESSIONS

Logical expressions allow you to specify more complicated rules for processing mail. For
example, you could specify that all mail from a certain domain with a size greater than a
certain amount be deleted unread unless a specific keyword were to be found in the header.

Logical expressions consist of the following operators, grouped in order of precedence:

┌──────────┬───────────────────────────────────────────┐
│ n │ integer constant │
│ $var │ variable. │
│/pattern/ │ regular expression. Evaluates as 0 or 1. │
├──────────┼───────────────────────────────────────────┤
│ ! │ logical not │
├──────────┼───────────────────────────────────────────┤
│ * │ multiply │
│ / │ divide │
├──────────┼───────────────────────────────────────────┤
│ + │ add │
│ - │ subtract │
├──────────┼───────────────────────────────────────────┤
│ < │ less than │
│ <= │ less than or equal │
│ > │ greater than │
│ >= │ greater than or equal │
├──────────┼───────────────────────────────────────────┤
│ == │ equal │
│ != │ not equal │
├──────────┼───────────────────────────────────────────┤
│ & │ logical AND │
│ && │ logical AND │
├──────────┼───────────────────────────────────────────┤
│ | │ logical OR │
│ || │ logical OR │
├──────────┼───────────────────────────────────────────┤
│ , │ comma │
└──────────┴───────────────────────────────────────────┘
Order of precedence in expression evaluation may be modified by use of parenthesis.

´:' commands may follow any close-parenthesis or regular expression. See examples below.

The second form of logical AND and OR operations ("&&" and "||") are optimized in this
way: If the left half of an AND is false, or the left half of an OR is true, then the
right hand is not evaluated. Thus, you should place a simple expression (such as a
subject match) to the left and a complex expression (such as a message body search) to the
right. If the simple expression evalutes to false or true respectively, the complex
expression is not tested.

The first form of logical AND and OR operations ("&" and "|") always test both sides of
the expression.

The comma operator deserves a bit of explanation for those not familiar with the C
language. The comma operator evalutes the expressions on both sides and returns the
expression on the right -- ignoring the one on the left. Thus, the expression "3 , 4"
evaluates as 4. The comma operator is useful only when the expression on the left has
some sort of side effect when evaluated -- i.e. it contains ':' commands.

Here are some sample expressions:

(/joe/f):m

mail from joe comes directly to me. This is the same as /joe/f:m

(/joe/f && /dive/s):+scuba

mail from joe with "dive" in the subject line goes to the scuba folder.

(/joe/f && !/dive/s):m
/joe/f:+scuba

mail from joe without "dive" in the subject line goes directly to me. Else, mail from joe
goes to the scuba folder.

(/joe/f && $lines > 1000):j

Looks like joe posted another long boring vacation report to the scuba list. Junk it.

(/earthlink/r && $size > 32768 &&
!(/key west/ia || /caymans/ia) ):j

Junk it if it came from or passed through earthlink (as shown by the Received: lines), and
the size is greater than 32k and it does not contain the phrase "key west" or "caymans"
anywhere in the message body. Case is ignored in the body search. Note that we examine
the message body last to avoid downloading the message unnecessarily.

Note also that logical expressions may be continued across multiple lines as needed.

(1):+maillog:c

An extremely simple expression. (1) is always true, so all mail that reaches this
expression is filed to the folder "maillog". The ":c" command causes processing to
continue.

This expression is a very good one to have at the top of your .sortmailrc when testing a
new configuration. All incoming mail is copied to a backup log before more complex
expressions are tested.

(/joe/f:+joemail && /scuba/:+scuba)

This example shows the use of ':' commands within an expression. Mail from joe goes to
the "joemail" folder. If it also contains the subject "scuba", it goes to the scuba
folder as well.

(/joe/f:+joemail , /scuba/:+scuba)

This example shows the use of the ',' operator. Mail from joe goes to the joemail folder.
Whether or not this matches, the mail is tested again to see if it belongs in the scuba
folder. If so, then processing is finished.

(/sex/:+sex && /drugs/:+drugs && /rock-n-roll/:+rock):+bacchanalia

This pattern does not do what it looks like it was intended to do. That is, at first
glance it looks as if the pattern is intended to place all messages containing "sex" in
the subject into the sex folder, all "drugs" messages into the drugs folder, all "rock-n-
roll" messages into the rock folder and place messages into the bacchanalia folder if they
match on all three keys. However, logical expressions are only evaluated as far as
necessary. If the "sex" pattern is not matched, the next two will not be tested at all.
A "rock-n-roll" message would be missed by this pattern.

In this case, the '&' operator should be used instead of '&&'.

MAILING LISTS

Skip this section unless you're using sortmail to administer a mailing list.

In a homogeneous environment, it is usually not necessary to use sortmail or any other
mail filter. You would simply create the alias in /etc/aliases and let sendmail(8) handle
everything.

However, in a heterogeneous environment, there can be problems. The internet document
Rfc822 specifies the handling of internet mail, but there are many mailers out there which
do not honor Rfc822 and cause trouble. Not surprisingly, many of the major service
providers are among the worst troublemakers.

What typically happens is that for some reason, some member of your mailing list suddenly
cannot receive mail. The service provider at the user's end bounces an error message back
to the list itself rather than to the original sender or the administrator. The error
message is then resent to the list subscribers -- including the the one who cannot receive
mail, causing another bounce. This creates a loop, sending and resending bounce messages
to everybody on the loop every few minutes. Murphy's Law states that this will happen
while you are on vacation.

Here is how to administer a mailing list:

First, (as root) edit /etc/aliases and add the following lines:

scubaclub: "| /usr/yourname/sortmail -sortmailrc scubaclubrc yourname"
scubaclub-real: :include:/usr/yourname/scubalist
scubaclub-request: yourname
owner-scubaclub: yourname

The first entry indicates that mail to the scuba club goes through sortmail, using a
specific sortmailrc file. The second entry is the actual scuba club alias to which
sortmail will forward the mail. The third entry is a standard list address which will be
used by users to contact you directly; this should always exist for any mailing list. The
final entry is used by the sendmail system to send internal errors back to you.

(Most unix systems require you to run newaliases(8) after editing /etc/aliases.)

Second, create /usr/yourname/scubalist, containing the names and addresses of everybody in
the list.
yourname <youraddress>
Joe Shmoe <[email protected]>
Jane Doe <[email protected]>
(etc.)

Third, create a sortmailrc file which will be used to filter incoming mail.

# general variables

set alias = scubaclub
set owner = yourname
set site = yourhost.com
set digestDir = ~/Maillists/Scubaclub

# mail that makes it through the filter gets mailed to
# the list and archived.
set default = m $alias-real@$site:a $digestDir/archive

# mail that gets rejected is mailed to me
set reject = m $owner

# catch anything that looks like a bounce or a loop

/Mailer-Daemon/f:m $owner
/MAILER-DAEMON/f:m $owner
/Postmaster/f:m $owner
/scubaclub/f:m $owner
/X-List-Name: scubaclub/h:m $owner
bouncecheck $digestDir/bounceDb

# (For some reason, we can't set Errors-To to $owner@$site,
# because if we do, sendmail will expand $owner into an
# invalid value before connecting to SMTP. It would probably
# be ok if I didn't have a personal .forward file. By adding
# a '\' to the address, we avoid the problem.)

replace Reply-To: $alias@$site
replace Errors-To: \\$owner@$site
header Comment: send add/delete requests to $alias-request@$site
header X-List-Name: $alias

In this example, the variables $alias, $owner, $site and $digestDir are not used
internally by sortmail, but are created for convenience and generality.

The search patterns are used to detect possible mail loops, and as such, always send mail
to the owner. Mail that makes it without matching any of the patterns is sent to the
list.

As a last resort, the mail is processed by the bouncecheck command which maintains a
database of previously-seen messages and will reject any message that seems to be a
repeat.

If mail passes through all the patterns unmatched, it is probably a valid message. In
this case, the message is processed by the commands in $other, which mail the message to
the actual alias, and append a digest version of the message to
~/Maillists/Scubaclub/archive.

Finally, the headers of outgoing mail are modified. The "Reply-To:" header is added so
that replies to mail from the list are sent to the list at large, and not just to the
sender of the original message. The "Errors-To:" header is added so that bounces will be
sent to the administrator instead of to the list in general. (Not all mail transfer
agents honor the "Errors-To:" header.)

The "X-List-Name:" header line serves two purposes. First, it lets recipients know what
they're receiving. Secondly, it is a trick used to help detect bounces. It is added so
that it may be searched for in incoming mail. If an incoming message contains this
header, it is likely that this is a bounce, and is sent to the administrator for
inspection.

If some of your list members wish to receive messages in "digest" form, you can split the
list into two sections, one normal and one for the members who want digests. Add the
following line to /etc/aliases:

scubaclub-digest: :include:/usr/yourname/scubadigest

and change $default in /usr/yourname/scubaclubrc:

set default = m $alias-real@foo:a $digestDir/archive:d $digestDir/digest

Now, incoming messages will be copied to ~/Maillists/Scubaclub/digest as well as to
~/Maillists/Scubaclub/archive. On a nightly basis, execute a program that will test to
see if ~/Maillists/Scubaclub/digest is non-empty, and if so, mail it to scubaclub-
digest@yourhost and empty it.

#! /bin/sh
#
# collect the digest file, prepend some header info and transmit

digest=/usr/yourname/Maillists/Scubaclub/digest
alias=scubaclub
host=yourhost.com

if [ ! -s $digest ] ; then
exit 0
fi

cat $digest | awk "
BEGIN {
print \"Return-Path: $alias@$host\"
print \"Date: `date`\"
print \"From: $alias@$host\"
print \"To: $alias@$host\"
print \"Subject: $alias digest\"
print \"X-List-Name: $alias\"
print \"\"
print \"\"
}
{print}" | \
/usr/lib/sendmail -om -oi -f$alias@$host $alias-digest

rm $digest
touch $digest
chmod a+w $digest

NOTES

Remember that sortmail can be executed under any userid (e.g. root, daemon or the sender
of the mail) depending on who sent the mail, and whether or not it came from the local
machine. Because of this, you cannot depend on any user environment to be available,
especially environment variables and path. All filenames and program names should be
specified as full paths, except that "~", "~user" and "+folder" forms are understood. The
permissions of sortmail and every directory along its path should be such that any user
can execute it.

If you pipe incoming mail through a program, that program should not generate any output
to stdout or stderr whatsoever. If it does, that output will be sent back to the
originator of the mail as if the mail had bounced.

Always test your setup thoroughly, especially when administering mail lists. Mistakes
usually result in bounce messages being sent to the originator of mail. This can be
catastrophic with a mail list. When testing a mail list, start with a test list
containing only your name and a known bad address to test bounce handling. Use of a
logfile and -v is recommended for the first few days after installing.

The bounce detection mechanism tries to be robust, but as the saying goes, you can never
make a system that's foolproof because some fools are ingenious. No matter how thorough
the detection mechanism is, there is a broken mailer out there somewhere that can defeat
it.

Never leave a mailing list unattended; that's when bounce loops always seem to start. If
you go on vacation, either temporarily shut the list down, or designate someone who can
turn it off in an emergency.

EXIT STATUS

The following exit values are returned:

0 Normal exit, mail delivered successfully.

1 Normal exit, but no messages waiting (-mbox and -pop options)

2 User error in command line options.

3 Error in .mailrc or .sortmailrc file.

4 Out of memory

5 Cannot determine user name

6 Cannot determine user directory

7 Cannot open a temporary file. In this case, sortmail attempts to recover by writing
the incoming mail to the user's inbox.

8 Cannot open bounce-check database (-dumpCrcs command)

9 Cannot open input file (-inbox option).

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