A simple SMTP server (in Python)

Question

Could you please suggest a simple SMTP server with the very basic APIs (by very basic I mean, to read, write, delete email), that could be run on a linux box? I just need to convert the crux of the email into XML format and FTP it to another machine.

Answer 1

Two python smtp servers I've used with success are:

1. Twisted's Mail - A very flexible mail library for SMTP, IMAP, ...
2. python-slimta - A complete MTA (smtp relay/forwarding server)

Twisted's example is shown below

# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

# You can run this module directly with:
#    twistd -ny emailserver.tac

"""
A toy email server.
"""
from __future__ import print_function

from zope.interface import implementer

from twisted.internet import defer
from twisted.mail import smtp
from twisted.mail.imap4 import LOGINCredentials, PLAINCredentials

from twisted.cred.checkers import InMemoryUsernamePasswordDatabaseDontUse
from twisted.cred.portal import IRealm
from twisted.cred.portal import Portal



@implementer(smtp.IMessageDelivery)
class ConsoleMessageDelivery:
    def receivedHeader(self, helo, origin, recipients):
        return "Received: ConsoleMessageDelivery"


    def validateFrom(self, helo, origin):
        # All addresses are accepted
        return origin


    def validateTo(self, user):
        # Only messages directed to the "console" user are accepted.
        if user.dest.local == "console":
            return lambda: ConsoleMessage()
        raise smtp.SMTPBadRcpt(user)



@implementer(smtp.IMessage)
class ConsoleMessage:
    def __init__(self):
        self.lines = []


    def lineReceived(self, line):
        self.lines.append(line)


    def eomReceived(self):
        print("New message received:")
        print("\n".join(self.lines))
        self.lines = None
        return defer.succeed(None)


    def connectionLost(self):
        # There was an error, throw away the stored lines
        self.lines = None



class ConsoleSMTPFactory(smtp.SMTPFactory):
    protocol = smtp.ESMTP

    def __init__(self, *a, **kw):
        smtp.SMTPFactory.__init__(self, *a, **kw)
        self.delivery = ConsoleMessageDelivery()


    def buildProtocol(self, addr):
        p = smtp.SMTPFactory.buildProtocol(self, addr)
        p.delivery = self.delivery
        p.challengers = {"LOGIN": LOGINCredentials, "PLAIN": PLAINCredentials}
        return p



@implementer(IRealm)
class SimpleRealm:
    def requestAvatar(self, avatarId, mind, *interfaces):
        if smtp.IMessageDelivery in interfaces:
            return smtp.IMessageDelivery, ConsoleMessageDelivery(), lambda: None
        raise NotImplementedError()



def main():
    from twisted.application import internet
    from twisted.application import service    

    portal = Portal(SimpleRealm())
    checker = InMemoryUsernamePasswordDatabaseDontUse()
    checker.addUser("guest", "password")
    portal.registerChecker(checker)

    a = service.Application("Console SMTP Server")
    internet.TCPServer(2500, ConsoleSMTPFactory(portal)).setServiceParent(a)

    return a

application = main()

Answer 2

There is Python SMTP server.

This module offers several classes to implement SMTP servers. One is a generic do-nothing implementation, which can be overridden, while the other two offer specific mail-sending strategies.