* C++ compiler - A C++ compiler is required.
* make - The GNU make is recommended. Solaris's make is to be avoided.
xBSD already has a gmake port, install it and use it (use gmake
everywhere this document refers to make).
* GDBM/DB - optional.
* The PCRE library (http:/www.pcre.org) is required.
* The Courier Unicode Library (http://www.courier-mta.org/unicode) must
be installed first.
* Courier Authentication Library - optional, for LDAP, MySQL, or
If the configure script detects that the Courier Authentication
Library is installed, support for courier-authlib gets automatically
compiled. Use the --disable-authlib option to manually disable
When courier-authlib support is enabled, the -d option to maildrop
will look up the account using the Courier Authentication Library,
making it possible to store mail account configuration in an LDAP,
MySQL, or a PostgreSQL database. See the courier-authlib documentation
for more information.
See http://www.courier-mta.org/authlib/ for more information.
When using the standalone maildrop build with courier-authlib, one
of the following configurations must be used:
* Your mail server must invoke maildrop as the root user (the -d
flag reads the mail account's uid and gid, then drops root).
* Manually change the permissions on the maildrop binary to be
* Manually change the permissions on the courier-authlib's socket
directory (/usr/local/var/spool/authdaemon by default) to be
globally readable or executable.
The default permissions on courier-authlib's socket directory blocks
world-access to the filesystem socket connected to courier-authlib's
authentication daemon process. In order for maildrop to connect to
the authentication library, maildrop must either have root
privileges (which will be temporary, as soon as maildrop determines
the account's userid and groupid, it will drop root, before reading
the maildroprc file), or courier-authlib's socket directory must
have world read and execute permission.
Note that if the permissions on the socket directory are changed,
anyone on the system can connect and obtain any account's password!
It is the system administrator's responsibility to choose the
appropriate security policy when using the Courier Authentication
When using the option to have maildrop invoked as root, an
additional option to automatically create a new account's home
directory becomes possible.
This uses the AUTH_MKHOMEDIR_SKEL environment variable. If this
environment variable is set, it must point to a template directory
such as /etc/skel. If the environment variable is set, and the
authenticated account's home directory does not exist, the contents
of the template directory get recursively copied into the new home
directory. The permissions of AUTH_MKHOMEDIR_SKEL and its contents
are preserved, and the owner userid and groupid is set to the
authenticated account's userid and groupid.
Consult your mail server's documentation for more information on how
to initialize the mail delivery agent's environment variables.
The typical sequence of commands to install maildrop is as follows. You
will likely need to use the GNU version of make. Other makes may not work.
See below for definition of various options to the configure script:
If the make command stops with syntax error in any Makefile, you probably
have an older make utility. See if you have a gmake command available. If
so, rerun configure as follows:
./configure [options] MAKE=gmake
Then execute the remaining commands, replacing make with gmake every time.
If make install-strip fails, try make install.
The configure script creates Makefile, and config.h. After running
configure, you may want to edit xconfig.h, and config.h in order to make
minor adjustments to the configuration.
Some versions of make may have problems handling the Makefile. If your
make gives you errors, try using the gmake command instead - the GNU make.
NOTE: configure attempts to automatically configure the following options
for maildrop according to your specific system. After running configure,
you should review these options and make any necessary adjustments.
WHAT GETS INSTALLED
If you're upgrading, read UPGRADING below.
The following assumes that the default options are used. The usual GNU
toolchain options can be used to relocate files from their default
locations (run ./configure --help for more information).
* /usr/local/bin - A number of binaries will be installed here, starting
with the main binary, maildrop, as well as additional utilities:
dotlock, maildirmake, makemime, reformail, and reformime. If certain
options are selected, some additional binaries may be installed here
* /usr/local/man - manual pages.
* /usr/local/include - C header files, for development, if the
--with-devel option is specified to the configure script.
* /usr/local/lib - C libraries, for development, if the --with-devel
option is specified to the configure script.
* /usr/local/share/maildrop/html - HTML versions of manual pages
installed in /usr/local/man.
These are the default directories. The defaults can be changed using the
standard autoconf options, run ./configure --help for more information.
From version 1.1 or earlier.
Read UPGRADE for some important notes. The default installation
directory/layout has changed.
From version 0.70 or earlier.
The --with-gdbm option has been renamed to --with-db. Its functionality
remains the same. The name change is due to some internal housekeeping.
From version 0.65, or earlier.
If possible, use a prebuilt package on platforms with a package manager
(rpm on Red Hat and derived distributions, deb on Debian, etc). If you've
been compiling and instaling maildrop manually, be aware of the following
changes when upgrading from 0.65 or earlier.
* The makegdbm utility has been renamed as makedat, to better reflect
the fact that it can be compiled with DB as well as GDBM database
* Config scripts from earlier versions usually created a Makefile that
automatically gzipped all manual pages during installation. This code
has been taken out. make install now installs uncompressed manual
pages only. If you do a make install, you'll need to go in and
manually remove gzipped manual pages from the previous version of
* You will need to have Perl 5 available to complete the compilation and
Operating system specific notes
This section will list any platform-depended issues.
This problem has been reported for Solaris 2.6. Other Solaris versions or
related platforms can be affected. Symptom - trying to run maildrop
results in an error message saying that libstdc++ cannot be opened.
Solaris's run time linker has a problem running C++ applications which
have the setuid or setgid bit set. On Solaris, libstdc++ (the runtime C++
library) is installed in /usr/local/lib. Solaris's runtime linker will
only open shared libraries in /usr/lib for programs with the setuid or
setgid bit set.
Maildrop is installed with the setuid and setgid bits set, so that
maildrop can change to the recipient's userid and group id. There are
three easy workarounds.
1. If you can configure your mail transport agent to set the correct user
and group IDs before running maildrop, maildrop will not need the
setuid and setgid privileges. After running make install-strip, go
ahead and manually turn these bits off for the maildrop, dotlock, and
2. Create a soft link from /usr/lib/localto /usr/local/lib, and add
/usr/lib/local to the LD_LIBRARY_PATH environment variable.
3. Create a soft link to libstdc++ from /usr/libto /usr/local/lib
Any sendmail platform
There are two quirks that anyone installing maildrop on a sendmail-based
system should be aware of.
* Unlike other mail transport agents, most sendmails completely discard
error messages from the local delivery agent. Therefore, you should
use the --enable-syslog=1 flag to configure on systems running
sendmail, unless you are very familiar with maildrop. Without this
flag, if you have any problems and maildrop is not installed
correctly, you will end up with a bunch of deferred mail, and
absolutely nothing to indicate why. Although maildrop will report an
error message, sendmail will discard the message without recording it
anywhere. With the --enable-syslog=1 option enabled, you at least get
to see the error messages in your syslog. However, please note that
syslog will now show any fatal maildrop errors resulting from botched
user recipe files.
* Interactive or background delivery mode. Usually the default sendmail
delivery mode is i - interactive, or b - background. It appears that
some versions of sendmail have a minor conflict with maildrop's
default security level. The conflict arises in a situation where a
local user sends a message to another local user. It appears that at
least some versions of sendmail invoke maildrop with the userid set to
the sender, and the -d option specifying the recipient. The default
maildrop configuration allows only certain "trusted" users to use the
-d option. What will happen is that maildrop will report an error, and
return an exit code to sendmail indicating a temporary error. The
message will be deferred, and on the next queue run, sendmail will
attempt to re-deliver it. But now, sendmail will do a queue run as
root, and root is allowed to use the -d option, so the message is
Note that this applies ONLY if you have maildrop defined as the local
delivery agent in sendmail.cf. This will happen if maildrop is invoked
from a .forward file. There are three possible solutions: do nothing,
since no real harm is done, local mail simply gets delivered with some
delay; you can change the default queueing method (in sendmail.cf) to
queue messages; or, you can specify --enable-restrict-trusted=0 option to
configure, and lift the restriction on the -d option. However, keep in
mind that the --enable-restrict-trusted=0 option allows a malicious user
use the -d option to mailbomb another local user's mailbox. This is why
the option is enabled by default. Of course, the same can also be
accomplished by funneling the mailbomb through sendmail, instead of
running maildrop directly. However, I can only tighten things up on my
end; I presume that throttling mechanisms are in place in sendmail to
block that avenue of attack.
Any AFS platform
If you're using AFS, it is possible that daemon processes will not even
have the read privileges on their effective userid's home directory.
maildrop likes to keep its temporary files in $HOME/.tmp, instead of
creating them in a shared public directory. You will need to specify the
--disable-tempdir flag when running configure, which configures maildrop
to use /tmp or /var/tmp for temporary file storage. (NOTE - this is
already a default option effective with maildrop 1.1)
Options to configure
Although most configuration is done as described in the following section,
I am migrating them to the configure script. Currently, configure support
the following options:
* --enable-DEBUG - specifying this parameter to configure enables some
debugging code. Used only by those who know how to use it. :-)
* --without-db - do not compile support for GDBM or DB databases.
Because supporting GDBM/DB databases significantly increases the size
of maildrop, GDBM/DB support can be omitted. If you do not have
GDBM/DB libraries, configure automatically disables GDBM/DB support.
Specifying --without-db disables the gdbmopen, gdbmclose, gdbmfetch,
and gdbmstore functions, and does not compile or install the
* --with-db=db - use the Berkeley DB library instead of GDBM. This
option will transparently use libdb.a instead of libgdbm.a. The
gdbmopen, gdbmclose, gdbmfetch, and gdbmstore functions work exactly
the same, but they will use libdb instead of libgdbm.
* --with-etcdir=directory - use the specified directory instead of /etc,
which is where maildrop expects to find some configuration files and
* --enable-syslog=1 - if specified, maildrop will log all fatal errors
to syslog(3). This is recommended for sendmail, which does not log
error messages for delivery agents.
* --enable-maildrop-uid=root and --enable-maildrop-gid=mail - sets the
userid and the groupid for the maildrop, maildirmake, and dotlock
programs. If not specified, they default to "root" and "mail"
respectively. See MAILBOX_MODE and RESET_GID below for more
* --with-devel - install development libraries and include files. This
option causes make install to copy over and install libraries, include
files, and manual pages, that are used by maildrop to parse and
process E-mail messages.
Most systems invoke the mail delivery agent and specify the account to
which the message is addressed. The mail delivery agent is a program
that's owned by root, and has the set-user-id bit set. The mail delivery
agent then immediately resets its userid to whomever the message is
Some mail systems run the delivery agent without specifying the recipient
on the command line. The user id is set by the mail system before running
the mail delivery agent. In this case, root privileges are not required,
and you may manually remove the set-user-id bit after installing maildrop.
Some mail systems may use group privileges in order to write to the system
mailbox directory. maildrop is installed with the set-group-id bit set as
well, and the mail group is assumed to be 'mail'. If a mail group other
than 'mail' is used, specify it via the --enable-maildrop-gid option. You
will also need to set the RESET_GID variable to 0 (see below). If
RESET_GID is left alone to its default value of 1, maildrop will drop any
acquired group ID right away, so its not necessary to remove the setgid
bit. maildrop attempts to detect if this is the case, but you always need
to confirm this.
* --enable-sendmail=program - sets the initial value for the SENDMAIL
environment variable for maildrop recipes. This is the pathname to the
default mail delivery agent. If this option is not specified,
configure will try to find it itself.
* --enable-lockext-def=extension - sets the initial value for the
LOCKEXT environment variable in maildrop. This is the filename
extension of dotlock files. The default is ".lock".
* --enable-locksleep-def=seconds - sets the initial value for the
LOCKSLEEP environment variable. This is how long maildrop waits before
trying to create a dotlock file again, if the dotlock file already
exists. The default is 5 seconds.
* --enable-locktimeout-def=seconds - sets the initial value for the
LOCKTIMEOUT environment variable. This is how long maildrop waits
before removing a stale dotlock file. The default is 60 seconds.
* --enable-lockrefresh-def=seconds- sets the initial value for the
LOCKREFRESH environment variable. This is how often maildrop refreshes
its own dotlock files, to keep them from going stale. The default is
See the manual page for maildropfilter for more information on these
* --enable-tempdir=directory - sets the name of a subdirectory in each
user's home directory where maildrop writes temporary files. maildrop
will create this directory, if missing. The default is .tmp.
* --disable-tempdir - do not use a subdirectory, instead create
temporary files in a shared /tmp or /var/tmp directory. May be
required on systems where daemon processes execute without privileges
to access shared filesystems. This is now the default option starting
with maildrop 1.1.
* --enable-smallmsg=bytes - sets the size of a message, in bytes, before
maildrop saves the message in a temporary file. Smaller messages are
read in memory, and filtered and delivered directly from memory. In
order to avoid consuming excessive amounts of expensive RAM, maildrop
saves larger messages in a temporary file. If the standard input to
maildrop is a file, a temporary file is not necessary. The default is
* --enable-global-timeout=seconds - sets numbers of seconds that
maildrop is willing to spend in order to deliver a single message.
This value becomes a hard coded limit. When the time expires, maildrop
terminates with an EX_TEMPFAIL error code. This is intended to stop
runaway mail filters. The default is 300 seconds (five minutes).
* --enable-crlf-term=flag - if set to 1, maildrop saves messages in the
mailbox with each line terminated by a carriage return/line feed
sequence. When set to 0, lines will be terminated by the linefeed
character only. The default value is 0.
* --enable-restrict-trusted=flag - if set to 1, maildrop permits only
certain "trusted" user or group IDs to use the -d option. Setting this
variable to 0 allows anyone to use the -d option (provided that
maildrop has set-userid-to-root privileges). This allows certain
denial-of-service attacks, so this setting is not recommended. The
default value is 1.
* --enable-keep-fromline=flag - if set to 1, when maildrop saves a
message to a mailbox file, it will use the same From_line address
which was present in the original message. If the original message
lacked a From_ line, maildrop will use the name of the user running
maildrop. If set to 0, maildrop will keep the original From_ line
address only if invoked by root, and reset it otherwise. The default
value of this option is the value of the --enable-restrict-trusted
option. Note that this option is new to maildrop version 0.54b. The
logic in the previous version of maildrop was always the same as if
this option was 0. Therefore, depending upon the value of the
--enable-restrict-trusted flag, you may find that maildrop behavior
changes with version 0.54b. This option also controls the semantics of
the -f option to maildrop (see below).
* --enable-trusted-users='...' - sets the list of users allowed to use
the -d option if --enable-restrict-trusted is set to 1. If
--enable-restrict-trusted is set to 0, this option is not used. Put a
list of user IDs allowed to use the -d option between the apostrophes,
separated by single spaces. If your mail transport agent uses maildrop
as the local delivery agent this list must include the userid that the
mail transport agent runs as. If this option is not specified,
maildrop attempts to put together a list including common mail system
* --enable-trusted-groups='...' - this is similar to the
--enable-trusted-users option, but specifies a list of group IDs
instead of user IDs. If --enable-restrict-trusted option is used, the
-d option will be permitted only if the real userid, of whoever's
invoking maildrop, is included in the trusted users list, OR if the
real groupid is included in the trusted groups list, OR if the
effective groupid is included in the trusted groups list.
CAUTION: the default configuration script installs maildrop with the
set group ID bit set, so that the effective groupid will always be the
same in the default maildrop configuration. If this group ID is
included in the trusted groups list, this effectively will allow
everyone to use the -d option.
The trusted groups feature has been implemented in order to add
additional flexibility in setting up a secure maildrop environment. If
the --enable-trusted-groups option is not used, the trusted groups
list is empty, so that the semantics of the trusted users option
remains the same as with previous versions of maildrop.
* --enable-use-flock=flag - if this option is set to 1, maildrop will
use either the flock(), the lockf(), or the fcntl() system call to
lock a mailbox file when delivering a message. On most systems, all
three use compatible locking mechanisms. In some very isolated cases,
flock(), lockf(), and fcntl(), are different, incompatible, locking
mechanisms. maildrop must use the same locking mechanism as any mail
reading programs. The configuration script will run some tests to
determine what locking function calls are available, and will choose
one by itself. The --with-locking-method can be used to manually
choose the locking function call to use.
* --with-locking-method=name - manually select a locking function call.
name is either "fcntl", "flock", or "lockf". Otherwise the
configuration script will pick one by itself.
* --enable-use-dotlock=flag - if this option is set to 1, maildrop will
create .lock files in order to gain access to the system mailbox file.
If this option is set to 0, maildrop will not use .lock files
automatically. However, the dotlock command can still be used to
manually create .lock files. The default value for this option is 1,
unless maildrop detects that the system mailbox directory does not
have the sticky bit set (set below), in which case the default option
is 0. maildrop attempts to figure out what the locking mechanism is
used by the mail reading programs. A mail reading program can only
create dotlock files in the system mailbox directory if the sticky bit
is set. Note, it is possible for both --enable-use-flockand
--enable-use-dotlock to be set to 1, in which case both locking
mechanisms are used simultaneously.
* --with-trashquota - include deleted messages, and the Trash folder, in
the estimated quota usage for maildirs. This should be used if related
packages (SqWebMail, Courier-IMAP) were also compiled with the
* --with-dirsync - after delivering a new message to a maildir
explicitly sync the maildir's directory directory. There's a school of
thought which believes that the Linux ext2 filesystem requires the
parent directory to be synced, in addition to the new message file
that's just been written to disk. There's another school of thought
that thinks that this issue is completely blown out of proportion, and
is really nothing more than a tempest in a teapot. However -- to
accomodate the former school of thought -- this option adds a little
bit of extra code to sync the parent directory.
Selecting an alternate C++ compiler
maildrop is written in C++. Some systems may have more than one C++
compiler available. If the default C++ compiler that's selected by the
configure script doesn't work, you may try an alternate C++ compiler.
First, you must extract the tarball again, into a different directory.
Then, before running ./configure, set the CXX environment variable to the
C++ compiler to be used. For example, to select the CC compiler:
$ export CXX
$ ./configure [options]
Then proceed as usual. The CXXFLAGS environment variable can also be used
to override compiler flags that configure selects.
Configuring the location of the system mailbox
When maildrop has a message to deliver to a user, maildrop must know where
user's mailbox is. Different systems use different places to store E-mail,
and different mechanisms to access it. And even on the same operating
system you may have variations due to different mail software.
Here are just some of the possible scenarios that may exist that maildrop
knows how to handle:
* All users' mailboxes usually are stored in a single directory, and the
name of the mailbox is the user name. On systems with many mailboxes,
the mailbox directory can be partitioned into a hierarchical tree,
based upon the initial letters of the user name. For example, the
mailbox for the user jtomas is /var/mail/j/jt/jthomas; mail for sjones
is stored in /var/mail/s/sj/sjones.
* Instead of storing mail in a separate directory, the system may store
incoming mail in each user's home directory.
* Instead of storing mail in a traditional mailbox file, the system may
implement a directory based format called maildir, that was introduced
in the Qmail mail server. With maildrop as your local delivery agent
you may implement the maildir format without having to use Qmail
itself. Maildir is a much more efficient mail storage format which
requires far less overhead. No locking of any kind is needed; multiple
instances of maildrop can dump mail into the same maildir at the same
* When mail is saved in a traditional mailbox file, only one program may
access the file at the same time. In order to synchronize access to
the mailbox file, the traditional mechanism uses a separate dot-lock
file. Newer systems may also use the flock() function on the mailbox
file itself. maildrop, by default, uses both mechanisms, except in one
case (see the --enable-use-dotlock option to configure, above), but
one or the other can always be selected to be used exclusively.
* Traditionally, the directory where system mailboxes reside has the
sticky bit set; all individual files are owned by their respective
users, with read/write permissions set for the user only, and
dot-locking is used to lock the mailbox. An alternative arrangement is
to remove the sticky bit from the directory, the directory has the
mail group ownership, and each mailbox is owned by the user, and the
mail group, with read/write privileges given to the owner. The mail
delivery agent runs under the user id, and the mail group id. This
allows the mail delivery agent to create new mailboxes, and have the
write permission on the user's mailbox. The flock() function is used
to lock an individual mailbox.
As you can see, there is a lot of variation in possible mail setups. It is
important that maildrop is configured to match your existing mail setup.
The configure script tries to automatically figure out the correct
settings, but you MUST always verify the output file, config.h, to make
sure that the settings are correct. Description of each variable defined
in config.hfollows. In addition, there are certain variables defined in a
different file, xconfig.h. These are settings that config.h cannot
This variable specifies the initial setting for the DEFAULT variable in
maildrop, which should be the location of the system default mailbox. If
DEFAULT_DEF begins with a slash, it should refer to a directory, and
maildrop will automatically append the user's name.
If it doesn't begin with a slash, maildrop will prepend the user's home
directory to DEFAULT_DEF. To use maildrop with qmail, which normally
delivers to $HOME/Mailbox, set DEFAULT_DEF to ./Mailbox.
The '=' character in DEFAULT_DEF gets replaced by progressive characters
from the user name of the user whose mail is being delivered. For example,
if mail to the user name "john" is delivered to /var/mail/j/jo/john and
mail to user "root" is delivered to /var/mail/r/ro/root, DEFAULT_DEF
should be set to /var/mail/=/== (maildrop automatically appends the full
user name as the last component).
If the DEFAULT_DEF/DEFAULT variable refers to a directory, maildrop
assumes that it is delivering the message to a maildir, otherwise maildrop
will deliver mail to a mailbox file, creating a new file if necessary.
maildrop does not deliver mail to flat directory, like procmail. If you
need to save messages in a directory, use the included program,
maildirmake, to create a maildir directory.
MAILBOX_MODE and RESET_GID
Here are the required setting in two of the most common mailbox
* Mailbox spool directory has the sticky bit set, mailboxes are readable
and writable by the user only - set MAILBOX_MODE to 0600, and
RESET_GID to 1.
* Mailbox spool directory does not have the sticky bit set, is writable
by the mail group ID, mailboxes are readable and writable by the user
ID - set MAILBOX_MODE to 0600, and RESET_GID to 0.
MAILBOX_MODE are the permissions maildrop uses to create new mailbox
files. If a mailbox file already exists, maildrop is not going to change
RESET_GID indicates whether maildrop should immediately drop any
set-group-id privileges. maildrop is installed with the set-group-id bit
set with maildrop's group id set to the mail group. If system mailbox
files have read/write access by both the user and the mail group, set
RESET_GID to 0 to keep the mail group ID, and specify the mail groupusing
the --enable-maildrop-gid flag to configure (see above).
If --enable-restrict-trusted option given to the configure script is set
to 1 (this is the default), maildrop allows only the users listed in this
environment variable to use the -d option. See the online documentation
for the description of the -d option.
Mail can be delivered in two different ways:
* The mail transport agent runs with root privileges. To deliver mail to
a local user, the mail transport agent runs maildrop after changing
the user id to the local user. In this case the -d option is not
* The mail transport agent runs as a non-privileged user. To deliver
mail to a local user, the mail transport agent runs the mail delivery
agent and specifies the user name with the -d option. The mail
delivery agent is expected to be a program with root privileges, and
it immediately must change its userid to the one specified by the -d
option. If this is the case, you must include the mail transport
agent's userid in the TRUSTED_USERS variable.
If --enable-restrict-trusted option given to the configure script is set
to 0, anyone can use the -d option. That is not recommended, it leaves
open a possibility for certain denial-of-service attacks.
Other configuration variables
The configure script also sets the following variables in autoconf.h.
After running the configure script, you may need to make some adjustments
to these variables also.
This variable in "autoconf.h" sets the initial contents of the PATH
variable, which is the initial system search path for commands invoked by
maildrop as child processes.
This variable in "autoconf.h" sets the initial contents of the SENDMAIL
variable, which is the local mail transport agent. maildrop runs this
program when instructed to deliver mail to a mailbox whose name begins
with the forwarding "!" character.
Other variables in autoconf.h
All the other variables are self explanatory, and rarely need to be
Using maildrop with sendmail
Maildrop can be easily used as sendmail's local delivery agent, instead of
procmail. Here is the suggested entry for sendmail.cf, courtesy of Eric J.
Mlocal, P=/usr/local/bin/maildrop, F=lsAw5:/|@SPfhn, S=10/30, R=20/40,
A=maildrop -d $u
You may also consider including the D, F, and M flags as well.
The -f option to maildrop
The -f option is new to version 0.55. The -f option sets the initial value
of the FROM variable. If no -f option is given, maildrop looks at any
From_ line in the message being delivered, otherwise it defaults to the
name of the user who invoked maildrop.
If the --enable-keep-fromline option is set to 0, anyone may use the -f
option. If --enable-keep-fromline is set to 1, only "trusted" users (as
defined by --enable-trusted-users) may use the -f option (ignored for
The initial value of the FROM variable is also used in the From_ line for
the message when maildrop saves it in a mailbox file. Although a recipe
may change the contents of the FROM variable, only the initial value gets
saved in the From_ line.
maildrop supports an alternative mail storage format called "maildir".
Unlike regular mailboxes, maildirs do not require locking, and are much
faster to use. Support for maildirs is not universal, but the number of
software packages that understands maildirs is constantly growing.
A maildir is a specially formatted directory, where messages are stored as
individual files, according to certain conventions. Use the maildirmake
command to create a maildir, with its structure and permissions properly
This creates a subdirectory in the current directory called "Maildir",
which is then prepared to store E-mail messages.
Maildir folder extension
This version of maildrop supports two extensions to the traditional
maidlir format: folders and quotas. The standard maildir format does not
support any kind of a folder hierarchy, and depends on the underlying
filesystem to enforce maximum usage quotas.
It is important to note that at this time not all maildir software
supports these extensions. Support is implemented mainly in other Courier
packages. Descriptions of these extension are freely available, hopefully
other software packages will add support for these extensions too.
Names of folders are limited by the maximum filename size of your
filesystem, and the names may not start with a period. Use the -f option
to maildirmake to create a new folder:
maildirmake -f Important ./Maildir
"./Maildir" must already be an existing maildir. The -f flag creates a
folder inside an existing maildir. A folder is just a subdirectory within
a maildir that is itself a maildir. The name of the subdirectory is the
folder name prefixed by a period. Also, the folder subdirectory contains a
zero-length file called "maildirfolder".
Maildrop can deliver to folders just like to regular maildirs:
Anywhere maildrop can deliver to a maildir, it can also deliver to a
See the manual page for maildirmake for more information.
Maildir quota extension
The quota extension allows maximum maildir quotas to be enforced where
filesystem-based quotas are not available, or cannot be used. This quota
mechanism has a number of limitations which are discussed in the manual
page for maildirquota, which contains more information.
Quota enforcement can be implemented by setting the MAILDIRQUOTA variable
in maildrop, as described in the maildirquota manual page.
Of course, quotas will be enforced only when maildrop is used to deliver
mail. Other applications, that do not understand the quota enhancement,
will not enforce any quotas. Mail delivered to a maildir by other
applications will not figure in quota calculation for some period of time.
Eventually, a regularly scheduled quota recalculation will pick them up
and include them in the current maildir quota.