Getting Started With Lamson

Lamson is designed to work like modern web application frameworks like Django, TurboGears,
ASP.NET, Ruby on Rails, and whatever PHP is using these days. At every design decision
Lamson tries to emulate terminology and features found in these frameworks. This Getting Started
document will help you get through that terminology, get you started running your first
lamson application, and walk you through the code you should read.

In total it should take you about 30 minutes to an hour to complete. If you just want
to try Lamson, at least go through the 30 second introduction given first.

The 30 Second Introduction

If you have Python and easy_install already, then try this out:

$ easy_install lamson
$ lamson gen -project mymailserver
$ cd mymailserver
$ lamson start
$ lamson log
$ nosetests
$ lamson help -for send
$ lamson send -sender -to \
        -subject “My test.” -body “Hi there.” -port 8823
$ less logs/lamson.log
$ mutt -F muttrc

You now have a working base Lamson setup ready for you to work on with the following installed:

When you’re in mutt during the above test run, try sending an email. The
included muttrc is configured to use the run/queue as the mail queue, and to
use the lamson sendmail command to deliver the mail. This tricks mutt into
interacting directly with your running Lamson server, so you can test the thing
with a real mail client and see how it will work without having to actually
deploy the server.

Finally, if you wanted to stop all of above you would do:

$ lamson stop -ALL run

Which tells Lamson to stop all processes that have a .pid file in the run directory.

Important Terminology

If you are an old SMTP guru and/or you’ve never written a web application with
a modern web framework, then some of the terminology used in Lamson may seem
confusing. Other terms may just confuse you or scare you because they sound
complicated. I tried my best to make the concepts used in Lamson
understandable and the code that implements them easy to read. In fact, you
could probably read the code to Lamson in an evening and understand how
everything works.

Experience has taught me that nobody reads the code, even if it is
small. Therefore, here are the most important concepts you should know to get
a grasp of Lamson and how it works.

Managing Your Server

Your Lamson application is now running inside the Lamson Python server. This is a very simple server based on Python’s
smtpd and asyncore libraries.

If you want to know more about how it operates, take a look at the lamson/ file in the source distribution.

You’ll need to use a few Lamson commands to manage the server. You already experienced them in the
30 second introduction, and you can review them all or see them
by using the lamson help command.

Right now you have Lamson running on port 8823 and a “Lamson logger” running on 8825. This means that
your lamson server (port 8823) will forward its messages to the logger (port 8825) thinking it’s your
real relay server. The truth is the logger just logs its messages to logs/logger.log and dumps it into
run/queue so you can inspect the results.

Before we learn how to manage them and what they do, open up the
config/ file and take a look:

from app.model import table
import logging

relay_config = {'host’: 'localhost’, 'port’: 8825}

receiver_config = {'host’: 'localhost’, 'port’: 8823}

database_config = { “metadata” : table.metadata, “url” : 'sqlite:///app/data/main.db’, “log_level” : logging.DEBUG

handlers = ['app.handlers.sample’]

router_defaults = {'host’: 'test\\.com’}

template_config = {'dir’: 'app’, 'module’: 'templates’}

Your file probably has some comments telling you what these do, but it’s important to understand
how they work.

First, this file is just plain old Python variables. It is loaded by one of
two other files in your config directory: config/ or
config/ The config/ file is started whenever you use the
lamson start command and its job is to read the config/ and
start all the services you need, then assign them as variables back to
config.settings so your handlers can get at them. The config/ is
almost the same, except it configures config.settings so that your unit tests
can run without any problems. Typically this means setting the spell checker
and not starting the real server.

Lamson can load any boot script you like, see Deferred Processing To Queues for an example of using this
to make a queue processor.

The important thing to understand about this setup (where a boot file reads and
then configures config.settings) that it makes it easy for you to change Lamson’s operations
or start additional services you need and configure them. For the most part you won’t need
to touch or until you need to add some new service, change the template
library you want to use, setup a different database ORM, etc. Until then just ignore it. Variables

The receiver_config variable is used by the lamson start command to figure out where to listen
for incoming SMTP connections. In a real installation this would be port 25 on your external
IP address. It’s where the internet talks to your server.

The relay_config setting is used by Lamson to figure out where to forward message replies (responses)
for real delivery. Normally this would be a “smart host” running a more established server
like Postfix or Exim to do the grunt work
of delivering to the final recipients.

The handlers variable lists the modules (not files) of the handlers you want to load.
Simply put them here and they’ll be loaded, even the lamson.handlers
modules will work here too.

The router_defaults are for the lamson.routing.Router
class and configure the default
routing regular expressions you plan on using. Typically you’ll at least configure the
host regular expression since that is used in every route and shouldn’t change too often.

Finally, template_config contains the configuration values for the templating system you’ll
be using. Lamson supports either Mako or Jinja2, but defaults to Jinja2.

Looking At config/

Programmers need to know how everything works before they trust it, so let’s look at the config/
file and see how these variables are used:

from config import settings
from lamson.routing import Router
from lamson.server import Relay, SMTPReceiver
from lamson.utils import configure_database
from lamson import view
import logging
import logging.config
import jinja2

  1. configure logging to go to a log file


  1. the relay host to actually send the final message to

settings.relay = Relay(host=settings.relay_config['host’], port=settings.relay_config['port’], debug=1)

  1. where to listen for incoming messages

settings.receiver = SMTPReceiver(settings.receiver_config['host’], settings.receiver_config['port’])

settings.database = configure_database(settings.database_config, also_create=False)


view.LOADER = jinja2.Environment( loader=jinja2.PackageLoader(settings.template_config['dir’], settings.template_config['module’]))

Don’t be afraid that you see this much Python, you normally wouldn’t touch this file
unless it were to add your own services or to make a new version for a different configuration.
For the most part, you can just edit the config/ and go.

First you’ll see that config/ sets up logging using the config/logging.conf
file, which you can change to reconfigure how you want logs to be created.

Then it starts assigning variables to the config.settings module that it
has imported at the top. This is important because after config.boot runs
your lamson code and handlers will have access to all these services. You
can get directly to the relay, receiver, database and anything else you need
by simply doing:

from config import settings

After that config.boot sets up the settings.relay, settings.receiver,
and settings.database. These three are used heavily in your own Lamson code,
so knowing how to change them if you need to helps you later.

After this we configure the lamson.routing.Router to have your defaults,
load up your handlers, and turn on RELOAD. Setting Router.RELOAD=True
tell the Router to reload all the handlers for each request. Very handy when you
are doing development since you don’t need to reload the server so often.

If you deploy to production, then you’ll want to set this to False since it’s
a performance hit.

Finally, the config.boot does the job os loading the template system you’ll use,
in this case Jinja2. Jinja2 and Mako use the same API so you can configure
Mako here as well, as long as the object assigned to view.LOADER has the same API
it will work.

Developing With Lamson

Now that you’ve received a thorough introduction to how to manage Lamson, and
how it is configured, you can get into actually writing some code for it.

Before you begin, you should know that writing an application for a mail server
can be a pain. The clients and servers that handle SMTP make a large number of
assumptions based on how the world was back in 1975. Everything is on defined ports
with defined command line parameters and the concept of someone pointing their
mail client at a different server arbitrarily just doesn’t exist.
The world of email is not like the web where you just take any old “client” and point
it at any old server and start messing with it.

Lucky for you, Lamson has solved most of these problems and provides you with a
bunch of handy development tools and tricks so you can work with your Lamson server
without having to kill yourself in configuration hell.

Using Mutt

You probably don’t have another SMTP server running, and even if you did, it’d
be a pain to configure it for development purposes. You’d have to setup aliases, new
mail boxes, restart it all the time, and other annoyances.

For development, what we want is our own little private SMTP relay, and since Lamson can
also deliver mail, that is what we get with the command:

$ lamson log

This tells Lamson to run as a “logging server”, which doesn’t actually deliver
any mail. With this one command you have a server running on 8825 that takes every
mail it receives and saves it to the run/queue Maildir and also logs it to
logs/logger.log. It also logs the full protocol chat to logs/lamson.err so
you can inspect it.

Lamson uses Maildir by default since it is the most reliable and fastest mail queue
format available. It could also store mail messages to any queue supported by Python’s
mailbox library. If you were
adventurous you could also use a RDBMS, but that’s just silly.

You also have the file muttrc which is configured to trick mutt into talking to your
running Lamson server, and then read mail out of the run/queue maildir that is filled
in by the lamson log server. Let’s take a look:

set mbox_type=Maildir
set folder=“run/queue”
set mask=”!\\.[.]”
set mbox=“run/queue”
set record=”+.Sent”
set postponed=”+.Drafts”
set spoolfile=“run/queue”
set sendmail=”/usr/bin/env lamson sendmail -port 8823 -host”

Notice that it’s configured sendmail to be “sendmail -port 8823 -host”
which is a special lamson sendmail command that knows how to talk to lamson and
read the arguments and input that mutt gives to deliver a mail.

Why does Lamson need its own sendmail? Because you actually have to configure most
mail server’s configuration files to change their ports before their sendmail command
will use a different port. Yes, the average sendmail command line tool assumes that it
is always talking to one and only one server on one and only one port for ever and all
eternity. Without lamson sendmail you wouldn’t be able to send to an arbitrary

With this setup (lamson start ; lamson log ; mutt -F muttrc) you can now
use your mutt client as a test tool for working with your application.

Stopping Lamson

The PID files are stored in the run directory. Here’s a sample
session where I stop all the running servers:

$ ls -l run/*.pid
-rw-r—r— 1 zedshaw staff 5 May 16 16:41 run/
-rw-r—r— 1 zedshaw staff 5 May 16 16:41 run/

$ lamson stop -ALL run
Stopping processes with the following PID files: ['run/’, 'run/’]
Attempting to stop lamson at pid 1693
Attempting to stop lamson at pid 1689

You can also pass other options to the stop command to just stop one server. Use
lamson help -for stop to see all the options.

Starting Lamson Again

Hopefully you’ve been paying attention and have figured out how to restart lamson and the
logging server. Just in case, here it is again:

$ lamson start
$ lamson log

You should also look in the logs/lamson.log file to see that it actually started. The
other files in the logs directory contain messages dumped to various output methods (like
Python’s stdout and stderr). Periodically, if the information you want is not in
logs/lamson.log then it is probably in the other files.

You can change your logging configuration by editing the logging line your config/ file.

Other Useful Commands

You should read the available commands documentation to get an
overview, and you can also use lamson help to see them at any time.


The first useful command is lamson send, which lets you send mail to SMTP servers (not
just Lamson) and watch the full SMTP protocol chatter. Here’s a sample:

$ lamson send -port 25 -host -debug 1 \
    -sender -to \
    -subject “Hi there” -body “Test body.”
send: 'ehlo zedshawscomputer.local\r\n’
reply: ’502 Error: command “EHLO” not implemented\r\n’
reply: retcode (502); Msg: Error: command “EHLO” not implemented
send: 'helo zedshawcomputer.local\r\n’
reply: ’250 localhost.localdomain\r\n’
reply: retcode (250); Msg: localhost.localdomain
send: 'mail FROM:\r\n’
reply: ’250 Ok\r\n’
reply: retcode (250); Msg: Ok
send: 'rcpt TO:\r\n’
reply: ’250 Ok\r\n’
reply: retcode (250); Msg: Ok
send: 'data\r\n’
reply: ’354 End data with .\r\n’
reply: retcode (354); Msg: End data with .
data: (354, 'End data with .')
send: 'Content-Type: text/plain; charset=“us-ascii”\r\nMIME-Version: 1.0\r\nContent-Transfer-Encoding: 7bit\r\nSubject: Hi there\r\nFrom:\r\nTo:\r\n\r\n.\r\n’
reply: ’250 Ok\r\n’
reply: retcode (250); Msg: Ok
data: (250, 'Ok’)
send: 'quit\r\n’
reply: ’221 Bye\r\n’
reply: retcode (221); Msg: Bye

Using this helps you debug your Lamson server by showing you the exact protocol sent
between you and the server. It is also a useful SMTP server debug command by itself.

When you use the supplied muttrc you’ll be configured to use Lamson’s sendmail
(not *send) command as your delivery command. This lets you use mutt as a complete development
tool with minimal configuration.


The lamson queue command lets you investigate and manipulate the run/queue (or any maildir).
You can pop a message off, get a message by its key, remove a message by its key, count the messages,clear the queue, list keys in the queue. It gives you a lower level view of the queue than
mutt would, and lets you manipulate it behind the scenes.


Lamson does reload the code of your project when it receives a new request (probably too
frequently), but if you change the config/ file then you need to restart.
Easiest way to do that is with the restart command.

Walking Through The Code

You should actually know quite a lot about how to run and mess with Lamson, so you’ll
want to start writing code. Before you do, go check out the API Documentation
and take a look around. This document will guide you through where everything is and how
to write your first handler, but when you start going out on your own you’ll need a good
set of reference material.

At the top level of your newly minted project you have these directories:

app — Where the application code (handlers, templates, models) lives.
config — You already saw everything in here.
logs — Log files get put here.
run — Stuff that would go in a /var/run like PID files and queues.
tests — Unit tests for handlers, templates, and models.

Lamson expects all of these directories to be right there, so don’t get
fancy and think you can move them around.

The first place to look is in the app directory, which has this:

app/data — Data you want to keep around goes here.
app/handlers — Lamson handlers go here.
app/model — Any type of backend ORM models or other non-handler code.
app/templates — Email templates.

You don’t technically have to store your data in app/data. You are free
to put it anywhere you want, it’s just convenient for most situations to
have it there.

Your app/model directory could have anything in it from simple modules for
working various Maildir queues, to full blown SQLAlchemy configurations for
your database. The only restriction is that you load them in the modules
yourself (no magic here).

The app/templates directory can have any structure you want, and as you
saw from the config.boot discussion it is just configured into the
Jinja2 configuration as the default. If you have a lot of templates it might
help to have them match your app/handlers layout in some logical way.

That only leaves your app/handlers directory:


This is where the world gets started. If you look at your config.settings
you’ll see this line:

handlers = ['app.handlers.sample’]

Yep, that’s telling the lamson.routing.Router
to load your app.handlers.sample
module to kick it into gear. It really is as simple as just putting the file in
that directory (in in sub-modules there) and then adding them to the handlers

You can also add handlers from modules outside of your app.handlers:

handlers = ['app.handlers.sample’, 'lamson.handlers.log’]

This installs the handler (lamson.handlers.log) that lamson uses to log every email it receives.

Writing Your Handler

This document is for getting started quickly, so going into the depths of the cool stuff
you can do with Lamson handlers is outside the scope, but if you open the app/handlers/
file and take a look you’ll how a handler is structured.

Since Lamson is changing so much the contents of the file aren’t included in this document. You’ll have to open it and take a look.

At the top of the file you should see your typical import statements:

import logging
from lamson.routing import route, route_like, stateless
from config.settings import relay, database
from lamson import view

Notice that we include elements from the lamson.routing that are decorators
we use to configure a route. Then you’ll see that we’re getting that settings.relay
and settings.database we configured in the previous sections. Finally we bring
in the lamson.view module directory to make rendering templates into email messages
a lot easier.

Now take a look at the rest of the file and you’ll how a handler is structured:

  1. Each state is a separate function in CAPS. It doesn’t have to be, it just looks better.
  2. Above each state function is a route, route_like, or stateless decorator to configure how lamson.routing.Router uses it.
  3. The route decorator takes a pattern and then regex keyword arguments to fill it in. The words in the pattern string are replaced in the final more complex routing regex by the keyword arguments after. However, if you want to use regex directly you can, route just needs a string that eventually becomes a regex.
  4. A state function changes state by returning the next function to call. You want to go to the RUNNING state, just return RUNNING.
  5. If any state function throws an error it will go into the ERROR state, so if you make a state handler named ERROR it will get called on the next event and can recover.
  6. If you want to run a state on this event rather than wait to have it run on the next, then simple call it and return what it returns. So to have RUNNING go now, just do return RUNNING(message, ...) and it will work.
  7. If a state has the same regex as another state, just use route_like to say that.
  8. If you have a stateless decorator after a route or route_like, then that handler will run for all addresses that match, not just if this handler is in that state.

That is pretty much the entire complexity of how you write a handler. You
setup routes, and return the next step in your conversation as the next
function to run. The lamson.routing.Router then takes each message it receives
and runs it through a processing loop handing it to your states and handlers.

How States Are Run

The best way to see how states are processed is to look at the Router code that does it:

    def deliver(self, message):
        if self.RELOAD: self.reload()

called_count = 0 for functions, matchkw in self.match(message['to’]): to_call = [] in_state_found = False for func in functions: if lamson_setting(func, 'stateless’): to_call.append(func) elif not in_state_found and self.in_state(func, message): to_call.append(func) in_state_found = True called_count += len(to_call) for func in to_call: if lamson_setting(func, 'nolocking’): self.call_safely(func, message, matchkw) else: with self.call_lock: self.call_safely(func, message, matchkw) if called_count == 0: if self.UNDELIVERABLE_QUEUE: LOG.debug(“Message to %r from %r undeliverable, putting in undeliverable queue.”, message['to’], message['from’]) self.UNDELIVERABLE_QUEUE.push(message) else: LOG.debug(“Message to %r from %r didn’t match any handlers.”, message['to’], message['from’])

What this does is take all the handlers you’ve loaded, and then finds which handlers have a state function that
matches the current message. It then goes through each potential match, and determines which of all the matching
state functions is “in that state”. This means that, even though you have six state functions that answer to
“(list_name)-(action)@(host)” only the one that matches the users current state (say PENDING) will be called next.
As it goes through these functions it also loads up any that are marked “stateless” so they can be called as well.

Finally, it just calls them in order. If the message results in no methods to call, then it will take the message
and tell you this, or put it into an UNDELIVERABLE_QUEUE for you to review it later.

Slight design criticism: Currently the order of these calls is fairly deterministic, but you can’t rely on it.
It’s also not clear if all matching states should run, or just the first. It currently only runs the first match,
but it might be better to run each match from each handler. Suggestions welcome on this.

Debugging Routes

In the old way of doing routing you would edit a large table of “routes” in your config/ file and
then that told Lamson how to run. The problem with this is it was too hard to maintain and too hard to
indicate that different states needed a different route.

The new setup is great because all your routing for each handler module is right there, and it’s easy to see
what will cause a particular state function to go off.

What sucks about the new setup is that you can’t find out what all the routes are doing globally in one
place. That’s where lamson routes comes in. Simply run that command and you’ll get a debug dump of
all the full routing regex and the functions and modules they belong to:

Routing ORDER:  [’^(?P<address>.+)@(?P<host>test\\.com)$’]
Routing TABLE: 
'^(?P<address>.+)@(?P<host>test\\.com)$’:  app.handlers.sample.START  app.handlers.sample.NEW_USER
   app.handlers.sample.END  app.handlers.sample.FORWARD  

This is telling you which regex is matched first, then what those regex are mapped to. This is very handy as you can copy-paste
that regex right into a python shell and then play with it to see if it would match what you want.

You can also pass in an email address to the -test option and it will tell you what routes would match
and which functions that will call:

osb $ lamson routes -test
2009-06-07 02:33:31,678 – root – INFO – Database configured to use sqlite:///app/data/main.db URL.
Routing ORDER: [... lots of regex here …]
Routing TABLE:
... each regex and what state functions it maps ..

TEST address '’ matches: '^(?P[a-zA-Z0-9][a-zA-Z0-9.]+)@(?Poneshotblog\\.com)$’ app.handlers.index.POSTING – {'host’: '’, 'post_name’: '’} '^(?P[a-zA-Z0-9][a-zA-Z0-9.]+)@(?Poneshotblog\\.com)$’ – {'host’: '’, 'post_name’: '’} '^(?P[a-zA-Z0-9][a-zA-Z0-9.]+)@(?Poneshotblog\\.com)$’ – {'host’: '’, 'post_name’: '’}
osb $

If you’re working with Lamson this is incredibly helpful, because it tells you what
routes you have, what functions they call, and then it’ll take an email address and
tell you all the routes that match it.


Lamson takes a lighter approach to how it runs. It assumes that most of the
time you want lamson to keep itself sane with minimal locking, and that you
want each of your state functions to run in a thread lock that prevents others
from stepping on your operations. In 95% of the cases, this is what you want.

To accomplish this, Lamson’s router will acquire an internal lock for
operations that change its state, and a separate lock before it calls each
state function. Since multiple state functions run inside each thread, but one
thread handles each message, you’ll get multiple processing, but each state
won’t step on other states in the system.

However, it’s those 5% of the times that will kill your application, and if you
know what you’re doing, you should be able to turn this off. In order to tell
the Router not to lock your state function, simply decorate it with
and Lamson will skip the locking and just run your state raw. This means that
other threads will run potentially stepping on your execution, so you must do
your own locking.

Now, don’t think that slapping a
on your state functions is some magic cure for performance issues. You only
ever want to do this if you really know your stuff, and you know how to make
that operation faster with better controlled locking.

The reality is, if you have an operation that takes so long it blocks
everything else, then you are doing it wrong by trying to do it all in your
state function. You should change your design so that this handler drops the
message into a
and that another Lamson server reads messages out of that to do the long
running processing.

Using queues and separate Lamson servers you can solve most of your processing
issues without a lot of thread juggling and process locking. In fact, since
Lamson uses maildir queues by default you can even spread these processors out
to multiple machines reading off a shared disk and everything will be just

But, since programmers will always want to just try turning off the locking,
Lamson supports the nolocking decorator. Use with care.

What’s In A Unit Test

Writing unit tests is way outside the scope of this document, but you should read up on using nosetests, testunit, and
you should look at lamson.testing for a bunch of helper functions. Also look in the generated tests directory
to see some examples.

Spell Checking Your Email Templates

Another big help is that Lamson has support for PyEnchant so you
can spell check your templates. You can use lamson.testing.spelling function in your unit tests.

Installing PyEnchant is kind of a pain, but the trick is to get the dictionary you want and put it in your
~/.enchant/myspell directory. You’ll also want to open the config/ file and uncomment the
lines at the bottom that tell PyEnchant where to find the enchant so (dylib).

PyEnchant is kind of hard to use, so if you have suggestions on a better Python spell checking lib for
unit tests please let me know.

Spam Filtering For Free

Lamson comes with the
lamson.spam module
which supports SpamBayes spam filtering

Read the document on Filtering Spam With Lamson to get
a full set of instructions on using the spam filtering features.

Other Examples

Next you’ll want to sink your teeth in a bigger example. Go grab the source distribution .tar.gz and
extract it so you can get at the examples:

$ tar -xzvf lamson-VERSION.tar.gz
$ cd lamson-VERSION
$ cd examples/osb

You are now in the osb example that is running on Using what you’ve learned so far
you can start reviewing the code and finding out how a working example

Getting Help

As you work through this documentation, send your questions to me and I’ll try to help
you. You can also join the mailing list and get help
from other Lamson users.