[Twisted-Python] newbie problem with SMTPClient

Dave Britton dave at davebritton.com
Mon Mar 2 15:57:17 EST 2009

I love the idea of twisted but I think I must have a twisted learning disability, as I have gotten nowhere in what ought to be a simple matter. 

I need to send out emails to small groups from my apache server running a python cgi using mod_python, but my hosting service doesn't have a MTA. Instead of learning how to install and configure exim I thought I would use twisted to make a simple mail client. I started with the tutorial example that appears at:


(.... is indenting)
============ tutorial code ================
import StringIO
from twisted.application import service
application = service.Application("SMTP Client Tutorial")
from twisted.application import internet
from twisted.internet import protocol
from twisted.internet import defer
from twisted.mail import smtp, relaymanager
class SMTPTutorialClient(smtp.ESMTPClient):
....mailFrom = "tutorial_sender at example.com"
....mailTo = "tutorial_recipient at example.net"
....mailData = '''\
Date: Fri, 6 Feb 2004 10:14:39 -0800
From: Tutorial Guy <tutorial_sender at example.com>
To: Tutorial Gal <tutorial_recipient at example.net>
Subject: Tutorate!

Hello, how are you, goodbye.
....def getMailFrom(self):
........result = self.mailFrom
........self.mailFrom = None
........return result
....def getMailTo(self):
........return [self.mailTo]
....def getMailData(self):
........return StringIO.StringIO(self.mailData)
....def sentMail(self, code, resp, numOk, addresses, log):
........print 'Sent', numOk, 'messages'
........from twisted.internet import reactor
class SMTPClientFactory(protocol.ClientFactory):
....protocol = SMTPTutorialClient
....def buildProtocol(self, addr):
........return self.protocol(secret=None, identity='example.com')
def getMailExchange(host):
....def cbMX(mxRecord):
........return str(mxRecord.exchange)
....return relaymanager.MXCalculator().getMX(host).addCallback(cbMX)
def cbMailExchange(exchange):
....smtpClientFactory = SMTPClientFactory()
....smtpClientService = internet.TCPClient(exchange, 25, smtpClientFactory)
============ end tutorial code ============

This nicely looks up the right MX record and sends out an email, just what I need. Now I want to expand it to allow me to give it a list of email addresses to send the message to (not just call this same routine multple times, which seems wasteful and slow and doesn't use twisted's power to process the multiple emails in multiple threads), but I'm having terrible trouble figuring out how to do that, which tells me I'm missing a paradigm somewhere, there's something I'm not getting.

Trouble 1 is figuring out the right way to pass additional parameters to callbacks. Is this right:

Dosomething(that-returns-a-deferred).addCallback(Then-do-the-next-thing, extra-parameter1, extraparameter2)

The function Then-do-the-next-thing() will receive the deferred returned results from Dosomething() as its first argument, and extra-parameter1 and extraparameter2 as the next two. That is as if calling:
Then-do-the-next-thing(Result-returned-by-Dosomething(),extra-parameter1, extraparameter2). Have I got this correct?

So, if this is right, then where do I want to put the additional argument that contains the next email address to send, if I iterate through the list and hand each one to the email sending process like this:

elist=['addr1 at domain.com','addr2 at nextdomain.com'...]
for e in elist:
.... e2={'mxhost':'','toaddr':e}
.... getMailExchange(e2).addCallback(cbMailExchange)

In the tutorial, getMailExchange() is passed just the domain of the addressee, and the sending out of the email happens when the callback returns the MX exchange. I changed that to split the email address, so now it returns both the full address and the mx:

def getMailExchange(addr):
.... host=addr.split('@')[1]
.... def cbMX(mxRecord):
.... .... return [addr,str(mxRecord.name)]
.... return relaymanager.MXCalculator().getMX(host).addCallback(cbMX)

At this point I can't figure out how to get the email address passed to wherever it needs to go. And I don't know really where it needs to go... yikes.

In the tutorial the actual email address is hard coded into the class SMTPTutorialClient(smtp.ESMTPClient) as a class attribute, mailTo. I need to change that to be variable.

How do I get this value (of mailTo) changed for each of the instances created by smtpClientFactory = SMTPClientFactory()? I think I must be confused about the roles of Factories and Protocols.

I can't seem to figure out a way that works to get the email address passed into the system as a variable. Rather than waste people's time by describing my various failures, I thought I'd just ask for suggestions about the right twisted way to do it. 

Thanks for any suggestions and directions!


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