On Thu, 09 Nov 2006 13:44:55 +0100, Jan Bakuwel <jan.bakuwel@int.greenpeace.org> wrote:

Hoi all,

This is my first message to the list so I think its appropriate to express my appreciation for all the excellent work done by the people who created & contributed to the twisted libraries.

I have a small but interesting problem that I'd like to ask your advise on, please see the description below. If you notice that I haven't understood something properly, I hope you'll correct me :-)

I've implemented a SMTP server (I've called it "xsmtp") using the twisted & python libraries. A MTA (Postfix) delivers email messages to the xsmtp server: the MTA opens a single SMTP session to the xsmpt server, then multiple "RCPT TO"s follow, one for each recipient.

As a result The "validateFrom" procedure is called by the twisted library once, followed by multiple calls to the "validateTo" procedure.

This is creating a small problem for me. Since I must process the email in the validateTo procedure, I will now receive multiple copies of the same email (albeit for different recipients). One of the tasks of the xsmtp server is to transmit these emails to another xsmtp server (SMTP cannot be used due to the inherently high latency connection between the two). Ideally I do not transfer the same email twice but would like to leave the delivery to multiple recipients up to the MTA on the other end. In a schema:

-> MTA -> xsmtp -- high latency link --> xsmtp -> MTA -> local delivery

To implement smtp.IMessageDelivery I have to provide for the following procedures:

validateFrom: called once shortly after SMTP session is initiated receivedHeader: called multiple times for each recipient validateTo: called multiple tiems for each recipient

One could say that "validateFrom" is the start of the process (of receiving an email) "receivedHeader/validateTo" is the core of the process. What I am missing is something that indicates the end of the process.

It would help me tremendously if smtp.IMessageDelivery would also provide an abstract method that is called once the message delivery is completed.

Any suggestions, thoughts are very welcome; perhaps this is already possible with the twisted libraries in a different way as I'm suggesting here?

The situation is not ideal, but I think if you use IMessageDeliveryFactory instead of IMessageDelivery you'll be able to accomplish your goal. With IMessageDeliveryFactory, you can create a new IMessageDelivery provider for each SMTP transaction. validateTo is still called multiple times on your IMessageDelivery provider, but because a new one is created for each transaction, you should be able to avoid making multiple deliveries to your real backend. (As I wrote that I realized it was not a very clear explanation at all, but I cannot think of another way to put it without actually implementing something). Jean-Paul