The PP X.400 Message Transfer Agent (MTA)

This is an X.400 Message Transfer Agent (MTA) written in the 1990s, I believe mostly by Steven Kille. This project was resurrected in 2024 by Jonathan M. Wilbur / Wildboar Software to be able to build using modern tooling on Linux in a Docker container. A few bugs were fixed as well.

Background: X.400 Message Handling Systems

X.400 Message Handling Systems were a messaging service similar in purpose to email--and, in fact, it competed with email at the time, though it lost--but devised by the International Telecommunications Union (ITU). It gets its name from the fact that the ITU's X.400-series of specifications, starting with ITU-T Recommendation X.400.

X.400 differs significantly by being a lot more technically complicated, but much more capable than email out-of-the-box, supporting things like binary data, encryption, authentication, integrity, read receipts, etc. While it has many benefits, it was designed to only utilize the extremely complicated OSI networking stack: it was never designed to run over TCP/IP, which was a big problem for its adoption. In addition to this, it uses attribute-value pairs for addressing, which makes the parsing, presentation, validation, and routing based on these addresses much more complicated than email's "user-at-host" addressing, which some have argued was a major reason for its downfall. It also has poor support for non-Romance language, but this could be said to be true of email as well.

Still, the X.400 MHS is used in NATO and Western militaries (I believe the U.S. and U.K. use it, at least), and in the Air Traffic Services Message Handling Services (AMHS) which is used by the aviation industry. I have also heard that it is still in use in the shipping / overseas transport industry for EDI, but I haven't confirmed this anywhere.

The PP X.400 MTA

PP is a Message Transfer Agent, intended for high volume message switching, protocol conversion, and format conversion. It is targeted for use in an operational environment, but is also be useful for investigating message related applications. Good management features are a major aspect of this system. PP supports the 1984 and 1988 versions of the CCITT X.400 / ISO 10021 services and protocols. Many existing IETF RFC 822 based protocols are supported, along with RFC 1148bis conversion to X.400. PP is an appropriate replacement for MMDF or Sendmail. This is the second public release of PP, and includes substantial changes based on feedback from using PP on many sites.

• PP is not proprietary and can be used for any purpose. The only restriction is that suing of the authors for any damage the code may cause is not allowed.
• PP runs on a range of UNIX and UNIX-like operating systems, including SUNOS, Ultrix, and BSD. A full list of platforms on which PP is know to run is included in the distribution.
• Current modules include:
  • X.400 (1984) P1 protocol.
  • X.400 (1988) P1 protocol.
  • Simple mail transfer protocol (SMTP), conformant to host requirements.
  • JNT mail (grey book) Protocol.
  • UUCP mail transfer.
  • DECNET Mail-11 transfer
  • Distribution list expansion and maintenance, using either a file based mechanism or an X.500 directory.
  • RFC 822-based local delivery.
  • Delivery time processing of messages.
  • Conversion between X.400 and RFC 822 according to the latest revision of RFC 1148, known as RFC 1148bis.
  • Conversion support for reformatting body parts and headers.
  • X-Window and line-based management console.
  • Message Authorisation checking.
  • Reformatting support for "mail hub" operation.
  • X.500-based distribution list facility using the QUIPU directory.
  • FAX interworking
• No User Agents (UAs) are included with PP. However, procedural access to the MTA is documented, to encourage others to write or to port UAs. Several existing UAs, such as MH, may be used with PP.
• It is expected that a Message Store to be used in conjunction with PP (PPMS), and an associated X-Windows User Agent (XUA) will be released on beta test in first quarter 92.
• The core routing of PP 6.0 is table based. DNS is used by the SMTP channel. The next version of PP will support Directory Based routing, which may use X.500 or DNS.
• PP 6.0 requires ISODE 7.0.
• X-Windows release X11R4 (or greater) is needed by some of the management tools. PP can be operated without these tools.
• The primary documentation for this release consists of a three and a half volume User's Manual (approx. 300 pages) and a set of UNIX manual pages. The sources to the User's Manual are in LaTeX format.

License

I believe this software was written before the standardized FOSS licenses even existed, but the authors left this in COVER-LETTER, which I interpret to be something like an MIT License:

PP is not proprietary and can be used for any purpose. The only restriction is that suing of the authors for any damage the code may cause is not allowed.

Documentation

This documentation describes how to configure, generate, and install the PP message system. It is intended only as a quick guide. The full details are in the PP documentation set - PP Manual: Installation and Operation. This can be found in the doc/manual/volume1 directory

Description

This is a description of how one can bring up the PP message system. It is assumed that you have super-user privileges in order to (re-)install the software. Super-user privileges are not required to configure or generate this software.

PP is normally installed with most programs and directories owned by a single user. Conventionally this username is "pp" and is not a normal user id but this is not required. You should normally do most of the compilation and configuration as this user.

Building

This requires (inclusively):

• A C compiler
  • The specific requirements are not known, but recent features are probably not needed, since this was written in the 1980s / 1990s!
  • TinyCC might suffice
• GNU Make
  • (Minimake might suffice)
• libgdbm libraries:
  • Which are:
    • libgdbm-compat-dev
    • libgdbm-compat4
    • libgdbm-dev
  • Which provide the ndbm.h header which you will be missing otherwise.
• libxaw7-dev
  • This is only needed if you are building MTAConsole and some other targets
• libxt-dev
  • This is only needed if you are building MTAConsole and some other targets
• groff
  • Needed for the nroff command, which is needed to create the tailor file, among other things.
• Docker, if you want to build the Docker image
• libisode
  • Provides OSI Networking
  • Build using this repository
• libdsap
  • Provides X.500 directory services
  • Build using this repository

Go to the config/ directory:

cd config

Select the Makefile and include-file skeletons which most closely match your system. The makefile skeleton has the extension .make, and the include-file skeleton has the extension .h. This will most likely be linux.make and linux.h respectively, in your case. Using Linux as an example:

cp config/linux.h h/config.h
cp config/linux.make ./Make.defs

You can configure the build further in these files as well as in ./OPTIONS.make.

Warning

This version of PP was designed against ISODE 7.0, and the original documentation says that it requires ISODE 7.0. However, it seems to run fine on ISODE 8.x and higher. Understand that there may be bugs as a result of this version breach. I (Jonathan Wilbur) have created many fixes to ISODE 8.0, so I would advise using that instead of ISODE 7.0.

It is assumed that you have ISODE 8.3.11 or higher installed on the machine in question, including the X.500 libraries libdsap libisode. If you wish to build the grey book channels for JANET mail, you should first build and install the unix-niftp package.

To build this, run this command EXACTLY from the root directory:

./make

This will cause a complete generation of the system. If all goes well, proceed with the installation. If not, complain, as there "should be no problems" at this step. It may be worth saving the output of the make stage in a file in case things do go wrong.

Installation

You will need to be the super-user to install the software. There are two kinds of activities: once-only activities that you perform the first time the software is installed; and each-time activities that you perform every time the software is installed.

The first once-only activity is to create the necessary basic directories to install the commands. This is done by issuing the command as super-user:

su
./make dirs

Note that the pp user id needs to have been allocated at this point.

The second once-only activity is to make sure that PP will run when when the machine goes multi-user. On Berkeley UNIX systems, add something along these lines to the /etc/rc.local file:

if [ -f /usr/lib/pp/pp.start ]; then
     /usr/lib/pp/pp.start & (echo -n ' pp') > /dev/console
fi

There are some examples of this start-up script in the config/ directory.

If you wish to use smtp then it may be appropriate to start the smtp server for /etc/inetd by adding a suitable line to /etc/inetd.conf. See Volume 1 for more details, but the basic format is something like:

smtp stream tcp nowait  pp  /usr/lib/pp/cmds/chans/smtpd
     smtpd /usr/lib/pp/cmds/chans/smtpsrvr smtp

To allow processes to contact the qmgr you must add a line to your isoentities file:

pickle "pp qmgr" 1.17.6.2.1 #1001/Internet=pickle+18000

You will need to replace "pickle" by your local host, and you may need to change the isomacro "Internet" to something else if you have a local ethernet or similar.

Alternatively you may add a suitable entry to the directory if this is being used as a nameserver. Some samples are given below the examples directory.

Then to install the following each-time activity is:

su
./make install

If you plan to run the MTAconsole program (and you should!) you will need to install the application defaults file. This is in the MTAconsole/ directory and it should be installed as MTAconsole in the app-defaults directory in your X hierarchy. For instance:

cd Src/MTAconsole
cp MTAconsole.ad /usr/lib/X11/app-defaults/MTAconsole

The same is true of the user utility xalert. This has a similar set of application defaults that should be installed.

That's about it. This will install everything. To clean-up the source tree as well, then use:

make clean

If this is the first time you have used PP it is worth picking one of the example configurations in the examples/ directory. Choose a sample that is close to your requirements as a starting point. The available samples are

• LOCALSMTP: Very simple local SMTP only
• JANET: A simple JANET configuration
• INTERNET: A simple Internet site, listening for SMTP messages

Change to one of these directories, and read the README there. This will tell you to do various things, depending on what configuration you have chosen. Remember, this is only an example and will not deal with all your needs.

After all is set up, and at regular intervals, you should check all is ok by running ckconfig (found in the tools directory) which will check things are installed correctly.

Tailoring

Tailoring is an essential part of running PP. This is somewhat complex to achieve the correct setup and so is described in Volume 1 of the PP manual. It is important that this is followed carefully.

Building Documentation

The directory doc/ contains the documentation set for this release. Consult the file doc/README for a description of each document. The directory doc/ps/ contains PostScript versions of each document. These can be used to generate standard documentation on PostScript printers, but users who want to preview the documentation should generate the .dvi files from the SLiTeX and LaTeX sources.

If you received this distribution from the network, then the directory doc/ps/ does not contain any PostScript files. There should be a separate compressed tar file, containing only PostScript files, available on the machine where you retrieved this distribution.

Support

I didn't write this software, I just resurrected it. If you would like support, please create an issue on the GitHub Issues page. Maybe one day, you'll be able to reach me over X.400, too! I welcome PRs, too.

Future Plans

I do not plan on doing much to improve upon this ancient codebase, however, I do plan to:

• Test it to make sure it actually works end-to-end
  • This is a huge ordeal, since it does not come with any X.400 client software of its own. I will have to write this myself.
• Create a Debian Package
• Create a Helm Chart

I might also try to get it building on other Linux distros, such as CentOS, Fedora, Arch, and Alpine.

Why "PP"?

I will quote an excerpt from Implementing X.400 and X.500: The PP and Quipu Systems by Stephen E. Kille:

PP is not an acronym. There is no truth in the rumour that PP stands for "Postman Pat," a famous British postman.

That's all I've got.

See Also

• ISODE - Which I also resurrected
• Meerkat DSA - A Free and Open-Source X.500 Directory I wrote. It has almost all official X.500 features and more. This repo also contains various X.500 libraries and tools, such as an X.500 command-line interface and an OSI networking library.
• Wildboar Software - A business pseudonym for Jonathan M. Wilbur, a computer nerd who also happens to sell a "Fail2Ban for Kubernetes" called Kube2Ban.
• M-Switch - I believe this is the closed-source and proprietary successor to PP, and I also believe this is maintained by Stephen E. Kille, or those who work for him.