Installing maildrop

# Requirements

- gcc that supports at least C++17 (http://www.gnu.org/software/gcc/)
- GDBM/DB - optional.
- The PCRE2 library (http:/www.pcre.org) is required.
- The Courier Unicode Library (https://www.courier-mta.org/unicode) must be installed first.
- The libidn2 library is required.

- Courier Authentication Library - optional, for LDAP, MySQL, or PostgreSQL support.

  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 courier-authlib support.

  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 https://www.courier-mta.org/authlib/ for more information.

  > NOTE:

  > 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 setuid root.
  > - 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 Library.

  > NOTE:

  > 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.

# Installing maildrop

## rpm and deb packages

These are not the same packages as the ones from various distributions' repositories. These packages carry a higher internal revision level in order to prevent them from getting upgraded by the distribution packaging, and their installation layout may differ from the distributions' preferred package installation layout. This packaging exists in order to have a convenient way of updating after a release without waiting for the distribution's package to get built, and to have a better correspondence with the documentation.

NOTE: If a distribution package is already installed it should be removed completely before switching to the upstream version (dnf remove or apt purge). Preserve any existing configuration files, beforehand, in order to restore it after switching packages. This applies to all Courier packages. A switch to this maildrop package requires switching the courier-unicode package (and possibility courier-authlib package) too.

NOTE: These packages use their own, generic, installation layout that may deviate slightly from the package installation conventions preferred by the distributions.

## rpm

Run `dnf install rpm-build` if it's not installed already, then:

    rpmbuild -ta maildrop-VERSION.tar.bz2

If this fails due to any missing dependencies, install them.

### Rocky/RHEL 8/9 notes

Courier packages require C++17 support, but the default version of gcc does not fully support it, and a newer gcc is needed:

    dnf install --enablerepo=crb -y gcc-toolset-14
    scl enable gcc-toolset-14 "rpmbuild -ta maildrop-VERSION.tar.bz2"

## deb

Run "apt install devscripts debhelper", if they're not installed already. Create an empty directory and copy/move the tarball into it:

    $ mkdir tmp
    $ mv maildrop-VERSION.tar.bz2 tmp
    $ cd tmp

Unpack the tarball and cd into the unpacked subdirectory:

    $ tar xvf maildrop-VERSION.tar.bz2
    $ cd maildrop-VERSION

Run the `courier-debuild` script, this is a wrapper for `debuild`, and it forwards its parameters to it:

    $ ./courier-debuild -us -uc

NOTE: the above steps must be followed strictly. The `courier-debuild` script expects the distributed tarball in its parent directory.

NOTE: if the courier-debuild script stops with an error complaining about missing dependencies, then use "apt install" to install them, then try again.

    $ DEBGCC=10 ./courier-debuild -us -uc

Setting the `DEBGCC` environment variable selects a non-default gcc version.

NOTE: All Courier packages should be built with the same version of gcc, which is selected by the `DEBGCC` environment variable before running `courier-debuild`. See courier-unicode's INSTALL for more information.

### Ubuntu and Debian

Courier packages require C++17 support, but the default version of gcc on Ubuntu does not fully support it, and a newer gcc is needed:

    $ sudo apt install -y gcc-10 g++-10
    $ DEBGCC=10 ./courier-debuild -us -uc

`make check` requires both the ISO-8859-1 based `en_US` locale in addition to the default `en_US.UTF-8`, on all versions of Ubuntu and Debian.

## Maintainer Mode (see README in the git repository to set up)

`make rpm` or `make deb`, as appropriate, will:

1. Increment an internal release number.

2. Run `make dist`.

3. Proceed and build a new release, creating the native packages in the rpm or deb subdirectory.

## Manual installation

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:

       ./configure [options]
       make
       make install-strip
       make install-man

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 as well.
- `/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.

## UPGRADING

#### 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 support.
- 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 maildrop.
- You will need to have Perl 5 available to complete the compilation and installation process.

## Operating system specific notes

This section will list any platform-depended issues.

#### Solaris

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 `reformail`.
2. Create a soft link from `/usr/lib/local`to `/usr/local/lib`, and add /usr/lib/local to the `LD_LIBRARY_PATH` environment variable.
3. Create a soft link to libstdc++ from `/usr/lib`to `/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 delivered.

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 `maildrop.makedat` utility.
- `--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 directories.
- `--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 information.
- `--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 addressed to.

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 15 seconds.

See the manual page for maildropfilter for more information on these variables.

- `--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 8192 bytes.
- `--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-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 user ids.
- `--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-flock`and -`-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-trashquota` option.
- `--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:

    $ CXX=CC
    $ 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 time.
- 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.h`follows. In addition, there are certain variables defined in a different file, x`config.h`. These are settings that `config.h` cannot automatically determine.

#### DEFAULT_DEF

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 environments:

- 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 its permissions.

`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).

#### TRUSTED_USERS

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 needed.
- 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.

#### DEFAULT_PATH

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.

#### SENDMAIL_DEF

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 changed.

## 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. Schwertfeger <ejs`@`bfd.com>:

    Mlocal,         P=/usr/local/bin/maildrop, F=lsAw5:/|@SPfhn, S=10/30, R=20/40,
                    T=DNS/RFC822/X-Unix,
                    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 everyone else).

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.

### Maildirs

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 set:

`maildirmake ./Maildir`

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:

`to "./Maildir/.Important"`

Anywhere maildrop can deliver to a maildir, it can also deliver to a maildir folder.

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.