NAME
avenger.local - deliver mail for a local user
SYNOPSIS
avenger.local [-f sender] [-D recip] [-a extra] [-d] user
DESCRIPTION
avenger.local is a local mail delivery agent that enables users to set
up multiple "extension" email addresses and process mail differently
for each addresses. The popular qmail MTA (<http://www.qmail.org/>)
has a mechanism for processing such extension addresses. avenger.local
provides a similar facility for users of other MTAs, such as sendmail.
To use avenger.local, you should configure your MTA so that it delivers
mail to user+extra@host by executing avenger.local -D user+extra@host
-d user+extra. Alternatively, you can execute avenger.local -a extra
-d user, but then you lose information about the host. However, the
latter syntax has the advantage of being command-line compatible with
procmail; thus, if your MTA has support for procmail as a local
delivery agent, you should be able to use that by simply substituting
avenger.local’s path for procmail’s.
Note that either way you invoke it, avenger.local rejects recipients
containing the string ".." in the local part. Such mailbox names are
not allowed by RFC822, and could potentially lead to security problems
if parts of mailbox names are used as file names. Out of paranoia,
avenger.local additionally rejects mailbox names containing the "/"
character in the extra portion after the local username.
avenger.local is designed to be unobtrusive for users who do not want
to take advantage of its functionality. When delivering mail for user,
if user’s home directory does not contain a subdirectory .avenger,
avenger.local simply executes the default mail delivery agent (usually
called mail.local).
For users who do have .avenger directories, mail is delivered according
to rule files called .avenger/local*. Mail to user@host is delivered
according to rules in .avenger/local. Mail to user+ext1@host is
delivered according to rules in .avenger/local+ext1 if such a file
exists, or else .avenger/local+default if such a file exists; if
neither file exists, the mail is bounced. Addresses containing
multiple "+" characters are handled as expected. Mail to
user+ext1+ext2@host is governed by, in order of decreasing precedence,
.avenger/local+ext1+ext2, .avenger/local+ext1+default, or
.avenger/local+default; it is bounced if none of those files exist.
Local rule files can be in one of two formats. If the first two
characters of the file are "#!", then the file is simply executed as a
script, with the message on standard input. The script’s standard
input will be read-only, but seekable, so, for example, the message can
be delivered to multiple mailboxes using the deliver utility.
Otherwise, if the first two characters of a file are not "#!",
avenger.local uses a syntax similar to (but not identical to) qmail’s,
where each line is one of the following types, depending on the first
character:
# comment
Lines starting with "#" are treated as comments and ignored. The
exception is that if the first line begins "#!", the file is
executed as a script. Note that if the first two characters of a
file are "#!" but the file’s execute permission bits are not set,
then mail sent to that address will be deferred. (This mechanism
can be used for intentionally deferring mail while performing
maintenance.)
./maildir/
/path/to/maildir/
A line starting "." or "/" and ending with a "/" character is
treated as a mail directory. Mail is delivered there using the
qmail maildir format.
./file
/path/to/file
A line starting "." or "/" and NOT ending with a "/" character
specifies an ordinary Unix mbox file into which the message should
be delivered.
&address
"&" indicates that a copy of the message should be forwarded to
address. You may not place a space between & and address, nor can
address contain angle brackets, comments, or anything other than an
email address with a fully-qualified domain name.
(Note that in qmail, the & character is optional for certain email
addresses, while avenger.local always requires the & character.)
Forwarding happens after all other lines in the file are processed.
If any other configuration line fails, for instance because a
command executed on behalf of a | line exits non-zero, the mail is
not forwarded to any of the addresses. (The exception is if a
command exits with status 99, in which case mail is forwarded to
addresses in all preceding & lines, but subsequent lines are
ignored.)
| command
Specifies that command should be run as a shell command, with the
mail message as its standard input. If command exits with a status
other than 0, processing of the local rule file terminates
immediately, with avenger.local’s exit status determined by
command’s.
If command’s status is 99, avenger.local exits with status 0,
effectively pretending the command just executed was the last line
in the .avenger/local* file. If command’s exit status is between
64 and 78, inclusive, avenger.local exits with the same status as
command. If command exits with status 100 or 112, avenger.local
exits with status 70. For all other exit values, or if command
terminates because of a signal, avenger.local exits with status 75.
Note that the --qmailexit flag changes this behavior, as described
below.
See the file /usr/include/sysexits.h for more information on the
meaning of various exit statuses to sendmail.
<address
<!command
This sets the envelope sender (i.e., bounce address) for copies of
the message forwarded to users with & lines. Note that one sender
address applies to all recipients, regardless of where in the
.avenger/local* file the bounce address is set. It is not possible
to forward from different bounce addresses for different
recipients.
The first form of this line simply sets the envelope sender to
address. No spaces are allowed between < and the address. No
angle brackets or comments are allowed either.
The second form of this line executes command with the shell,
giving it the message body as standard input. If command exits
with status 0 and outputs exactly one line of text, this line will
be interpreted as the new envelope sender for forwarded copies the
message. If command exits with any of statuses 64-78, 99-100, or
111-112, processing of the avenger/.local* halts exactly as for the
| command. For other exit statuses, or if command outputs no lines
or more than one line, the command’s result is ignored and
processing continues with the envelope sender unchanged.
! command
Runs command with the shell, giving it the mail message on standard
input. If the command exits 0 and outputs exactly one line of text
beginning "." or "/", the output is interpreted as either a maildir
(if the line ends "/") or a mailbox (if it doesn’t) to which the
message should be delivered. In other cases, either the ! line is
ignored, or processing halts, as described for the <! command.
A completely empty file (not even containing a comment or blank line),
or a missing .avenger/local (with no extension file), is treated as
equivalent to a file with the line "./Mailbox".
OPTIONS
-a extra
Specifies the extra portion of the local part of the email address
after the user name. In other words, if avenger.local is invoked
with arguments -a extra -d user, it is equivalent to invoking it
with the arguments -d user+extra. The -a option allows command-
line compatibility with sendmail’s procmail interface, which
separates out the user name from the extension portion of the
address.
-d user
Specifies the local user to deliver mail to. Note that for
compatibility with other local mailers, the -d is optional, you can
simply specify user as the final command-line argument.
-f sender
-r sender
The -f option specifies the envelope sender of the message. For
historical reasons, -r is synonymous with -f.
-t This option is silently ignored, for command-line compatibility
with procmail.
-B Ordinarily, when forwarding a bounce message, avenger.local will
invoke sendmail with the argument -f followed by an empty string
argument (i.e., specifying an empty from address). This does not
work with some older versions of sendmail. The -B option says that
bounce messages should be forwarded with arguments -f @ instead,
which appears to produce the desired (MAILER-DAEMON) result with
older versions of sendmail.
-Y This option is silently ignored, for command-line compatibility
with procmail.
--fallback program
If the user specified on the command line does not exist or have a
$HOME/.avenger/ directory, or else has UID 0 (root), or has an
invalid shell or an expired account, then avenger.local will not
attempt to deliver mail to the user. Instead, it will attempt to
run the system’s normal mail delivery agent as a fallback. This
program is usually called mail.local, but you can specify an
alternative with the --falback option. Note that this should be
the full path of the program, and should not contain any arguments.
avenger.local will supply the arguments -f from -d user.
--fcntl
This option enables fcntl (a.k.a. POSIX) file locking of mail
spools, in addition to flock and dotfile locking. The advantage of
fcntl locking is that it may do the right thing over NFS. However,
if either the NFS client or server does not properly support fcntl
locking, or the file system is not mounted with the appropriate
options, fcntl locking can fail in one of several ways. It can
allow different processes to lock the same file concurrently--even
on the same machine. It can simply hang when trying to acquire a
lock, even if no other process holds a lock on the file. Also, on
some OSes it can interact badly with flock locking, because those
OSes actually implement flock in terms of fcntl. For these
reasons, avenger.local performs dotfile and flock locking by
default, but not fcntl locking.
--qmailexit
When programs from |, !, and <! exit with non-zero exit status, the
--qmailexit flag causes avenger.local to translate the exit codes
to ones more suitable for qmail. Any code that would cause a hard
error in sendmail causes avenger.local to exit with 100, any soft
error causes exit code 111, and exit code 99 is passed through.
--sendmail program
Specifies the program to run to send mail, when users have lines
beginning "&" in their .avenger/local* files. If program contains
spaces, it is broken into multiple arguments. The default value
for program is "sendmail -oi -os -oee".
--separator char
Specifies a separator character to place between portions of the
address extension. The default value is "+". Thus, the argument
-a a+b would cause avenger.local to search for files
$HOME/.avenger/local+a+b, $HOME/.avenger/local+a+default, and
$HOME/.avenger/local+default. Specifying a different char, say
"-", would change the "+" to "-" in both the email address and file
names.
--smuser user
By default, sendmail is run as the user under which avenger.local
is invoked, which will ordinarily be root. To drop privileges
before running sendmail, you can specify this argument and
avenger.local will run sendmail as user. Note that avenger doesn’t
run sendmail as the recipient user, because this often results in
undesirable "X-Authentication-Warning" fields in the header. If
you wish the header to reflect a trail of how a message has been
forwarded, see the --to option below.
--tmpfile template
avenger.local creates a copy of the message in a local file.
template is a template for the name of the file, which must end
with a number of "X" characters, which will be replaced by a unique
identifier. (This is for use with the mkstemp(3) library call.)
The default value is "/tmp/msg.XXXXXXXXXX".
--to address (-D address)
Specifies the full envelope recipient address to which this message
is being delivered. With this option, avenger.local adds a line
"Delivered-To: address" to the header of the mail message. It
also checks that the header did not previously contain the same
line--if the message has already been delivered to the same
address, this indicates a loop, and avenger.local exits with status
70.
ENVIRONMENT
The following environment variables are set when running commands
specified in lines starting |.
EXT The local portion of the email address following the first
separator character (which is the "+" character, unless set
otherwise by --separator). This variable is not set if there is no
extension in the email address.
EXT1, EXT2, ...
When EXT itself contains a the separator character, EXT1 contains
the part of EXT after the first separator, EXT2 the part after the
second separator, and so on for each separator character in EXT.
HOST
If a recipient has been specified with the -D recip flag, this
variable will contain the host portion of recip.
LOCAL
If a recipient has been specified with the -D recip flag, this
variable will contain the local portion of recip.
PREFIX
SUFFIX, SUFFIX1, SUFFIX2, ...
Assuming the separator is "+", when processing a file
local+base+default, PREFIX is set to base, while SUFFIX is set to
the portion of the name for which default was substituted. When
the file does not end with default, SUFFIX is not set. When the
file is just local with no extension, neither PREFIX nor SUFFIX is
set. When SUFFIX itself contains a "+" character, SUFFIX1 contains
to the part of SUFFIX after the first "+" character, SUFFIX2
contains the part after the second "+", and so on for each "+"
character in suffix.
RECIPIENT
If the --to option was specified, the RECIPIENT environment
variable is set to the address specified in that option.
Otherwise, RECIPIENT is not set.
RECIPIENT_HOST
RECIPIENT_LOCAL
These are the same as HOST and LOCAL, but with all characters
folded to lower-case.
RPLINE
A "Return-Path:" line suitable for prepending to the message
header.
SENDER
The envelope sender of the message.
SENDMAIL
The value of the --sendmail option, or "sendmail -oi -os -oee" by
default.
SENDFROM
This is the same as $SENDER, unless envelope sender is empty (for a
bounce message) and the -B option has been specified, in which case
SENDFROM is "@". You can forward a message on from the same sender
with a line like this:
| $SENDMAIL -f "$SENDFROM" -- recpient1@host1.com ...
SEPARATOR
The separator character specified by --separator, or the default
"+" if none has been explicitly specified.
UFLINE
An mbox "From " line suitable for prepending to the message before
appending it to a mailbox or passing it to a filter that expects
such a line.
USER
The user to whom the message is being delivered.
EXAMPLES
To use avenger.local with sendmail, you might put the following in your
sendmail m4 configuration file (this is the file ending .mc that
produces your sendmail.cf file):
FEATURE(`local_procmail',
`/usr/local/libexec/avenger.local',
`avenger.local -a $h -d $u')
To deliver mail to a maildir directory called inbox in your home
directory, you would place the following line in the file
$HOME/.avenger/local:
./inbox/
If you are subscribed to several mailing lists, you might wish to spool
them in separate files, so as to read them separately. (For example,
the emacs editor has a newsreader, GNUS, that lets you read multiple
mailboxes more like newsgroups.) To do this, you should subscribe to
each mailing list under a different address. If your address is
user@host, you might subscribe to the Mail Avenger mailing list as
user+avenger@host. To spool mail in file
$HOME/Mail/incoming/avenger-list.spool, create a file
$HOME/Mail/.avenger/local+avenger with the following line:
./Mail/incoming/avenger-list.spool
To create a mailing list user+friends@host for yourself and your
friends, create a file $HOME/Mail/.avenger/local+friends with your
inbox and their addresses, for example:
./inbox/
&friend1@host1.com
&friend2@host2.com
FILES
/usr/local/libexec/avenger.local, $HOME/.avenger/local,
$HOME/.avenger/local*, /etc/mail/sendmail.cf,
/usr/local/share/avenger/avsendmail.m4
SEE ALSO
avenger(1), deliver(1), dotlock(1), mail.local(8)
The Mail Avenger home page: <http://www.mailavenger.org/>.
BUGS
avenger.local doesn’t necessarily report problems in a the most useful
place when it encounters errors in a .avenger/local* file. It does
send some diagnostics to standard error, but these will typically end
up in the mail log or in bounce messages returned to the sender.
avenger.local should always provide the exact envelope recipient in the
RECIPIENT environment variable. Unfortunately, this information is not
available unless it has been supplied with the -D flag. Often the
envelope recipient is just "${USER}${SEPARATOR}${EXT}@your.host.name",
but it might not be if there are aliases or virtual domains. On
servers with virtual hosts, the actual hostname used will be
unavailable in the general case (though you may be able to deduce it
from $USER and $EXT if you know your particular setup). Note that it
is possible to configure sendmail to supply the full recipient address.
Mail avenger comes with example sendmail configuration directives that
can be included in your sendmail.mc m4 configuration file; see
/usr/local/share/avenger/avsendmail.m4.
To protect against concurrent accesses to mbox format files,
avenger.local uses both flock and dotfiles to lock mailboxes. However,
it does not use fcntl/lockf-style locking by default. Thus, if your
mail reader exclusively uses fcntl for locking, there will be race
conditions unless you specify the --fcntl option.
AUTHOR
David Mazieres