@hackage postmaster0.1

Postmaster ESMTP Server

Categories
- Network Development
License
LicenseRef-GPL
Maintainer
Peter Simons <simons@cryp.to>
Links
- Homepage
- Documentation
- No source repository
- Security
Versions
- 0.3.3 Fri, 6 Sep 2019
- 0.3.2 Wed, 24 May 2017
- 0.3.1 Wed, 24 May 2017
- 0.3 Tue, 12 Feb 2013
- 0.2 Fri, 26 Feb 2010
- 0.1 Wed, 20 Feb 2008

Installation
In your cabal file:
Dependencies (0)
Dependents (1)
@hackage/acme-everything

Postmaster ESMTP Server

:Latest Release: postmaster-0.1.tar.gz_ :Darcs: darcs_ get http://postmaster.cryp.to/ postmaster

.. contents::

The Sales Pitch

Postmaster is the mail transport agent of choice for the discriminating hacker. Or, to be more accurate: for the discriminating Haskell_ hacker, because if you don't know any Haskell, you have about zero chance of running this software right now. I plan on turning Postmaster into something an end-user can run, but that's a long road.

So why yet another MTA? Aren't Sendmail, Qmail, Postfix, and Exim enough already?

No, unfortunately they are not, because none of those programs comes even close to the degree of configurability I need. Postmaster allows you to configure anything. I really mean it. You'd like to configure your MTA to do mail relaying for the site example.org only on Saturdays in a leap year? No problem at all. You'd like to put your entire mail configuration into a DNS zone and distribute it through the domain name system to your mail exchangers? Be my guest. You'd like to rewrite the word "no" to "yes" in any e-mail you receive which has "Michelle" in the From: header and was sent between 8am and 10am CET? Sure thing.

Postmaster is not really an MTA, it is a framework in which you can easily write your own, custom-built MTA! This means that Postmaster contains everything except for the routine main. That's what you have to write.

What can it do? '''''''''''''''

Postmaster implements an ESMTP server. Given a configuration, it starts up and listens for incoming SMTP connections, handles them, and pipes the accepted e-mail messages into an arbitrary local mailer of your choice. A good local mailer is Procmail_.

Beyond that, you can configure and modify every little step of the SMTP transaction. All the real work is done through a call-back function. Postmaster triggers an "event" every time a state change is required, and hopes that the call-back does whatever is necessary. Among the known events, this one is popular::

AddRcptTo Mailbox

So by writing a handler function for this event, you can configure what user addresses the server will accept. For example::

joe, jane :: Mailbox
joe  = Mailbox [] "joe"  "example.net"
jane = Mailbox [] "jane" "example.net"

admin :: Mailbox
admin = Mailbox [] "janes.husband" "example.com"

event :: Event -> Smtpd SmtpReply
event (AddRcptTo mbox)
  | mbox == joe  = procmail mbox "joe" []
  | mbox == jane = do
      from <- gets mailFrom
      when (from == joe)
        (relay [admin] >> return ())
      procmail mbox "jane" []
  | otherwise    = say 5 5 3 "unknown recipient"

You could also read that configuration from a file, query the DNS for that recipient, or accept / refuse addresses randomly. It's entirely up to you.

Postmaster provides a wealth of SMTP-related functions you can use. You can (asynchronously) resolve A, PTR, or MX records. There is a generic, type-safe Unix-like environment for each session and a global one for the entire daemon in which you can store any data your event handler needs. Postmaster provides a framework for logging messages through syslog(3). And, last but not least, there is a rapidly growing collection of re-usable event handlers which you can plug together to configure complex setups in a few lines of code.

What can it not do? '''''''''''''''''''''

At the moment, Postmaster has no mail queue. Until that is implemented, there is no way to deliver outbound messages via SMTP. If you have to relay e-mail for others, you will need another MTA installed to do that. Sendmail_ is particularly well suited for the task. Just modify your sendmail.mc file to contain the lines ::

FEATURE(no_default_msa)
dnl DAEMON_OPTIONS(`Port=25, Name=MTA')
DAEMON_OPTIONS(`Port=587, Name=MSA, M=E')

and your submit.mc file to contain::

FEATURE(`msp', `', `MSA')

This configures Sendmail to act as a "mail submission agent". Meaning that it will not listen on port 25 but on port 587 instead. Correspondingly, your local mail system will not inject messages via localhost:25 but localhost:587. You'll effectively use Postmaster as your MTA to the outside world, and Sendmail as your MTA on the inside. It's not beautiful, but it will work very reliably until Postmaster's own delivery agent is ready.

Documentation

Postmaster Tutorial_ A walk through "Config.hs" -- this is work in progress.

Reference Documentation_ Haddock-generated reference of all exported functions.

Building Postmaster

To compile the software, you need GHC_ version 6.6 or later (only tested with GHC 6.8.x). Furthermore, you'll need the GNU adns_ and OpenSSL_ C libraries installed.

You can install through your distro, if it provides postmaster, or from source. The source can be gotten from the Darcs repo or Hackage.

Once you've fetched the sources, do the following:

Build and install through Cabal as for other Haskell packages:

runhaskell Setup configure --user --prefix=$HOME runhaskell Setup build runhaskell Setup install --user

(You may want to remove the --user flag when installing as root.)

You can also install via the GNU Autotools.

Edit GNUmakefile to fit your system. You'll have to adapt the variable HDI_PATH to point to the base directory where the Haddock interface files for your compiler are installed or the documentation won't (re-)build.
Say make. You need GNU make to build Postmaster, so if you're running a BSD Unix, gmake should be used instead.
If you get this compiler error::

.objs/Digest.o(.text+0x357): In function spyU_info': : undefined reference to EVP_mdc2'

then your OpenSSL version doesn't contain the MDC2 hash algorithm yet. That's no problem ... just comment out the (three or so) references to it in hopenssl/Digest.hs -- or upgrade to OpenSSL 0.9.7e or later.