[Sussex] PHPSMTPD - tests anyone?

[Steve Dobson]

Hi Ronan

On Thu, Sep 15, 2005 at 02:35:34PM +0100, Ronan Chilvers wrote:
> But the idea behind this software is NOT to be an MTA, its to allow it
> to speak SMTP so it can take advantage of the interface.
> 
> A common way for autoresponders to work is to define a transport from
> the MTA to the autoresponder interface, whatever way you do it (in my
> case via SMTP which is incidentally, nothing new in the world of
> autoresponders).

I agree that autoresponders have a transport from the MTA to their
interface.  I'm thinking of mailman and the like here, systems which
are designed to work via email but where you don't "talk" to a human.

But I disagree that using SMTP for an MTA to talk to an autoresponder
is logical.  If you're listening on port 25 (the SMPT port) then no
other process, i.e. a real MTA, can be.

If you're listening on a non-standard port (which having just read your
page suggest that this is the way you plan on using it) then this makes
a little more sense, but it still isn't, IMO, a good way to do things.
Think about it, at some point you'll have two copies of the e-mail in
memory, the one in the MTA and the one being passed on to PHPSMTPD -
not very efficient.  Two copies of the mail in memory, three extra
sockets and a whole separate process running, just to copy an incoming
e-mail to a file.  I can do that in about a dozen lines in exim config.

> You then define an alias map which replicates mail to
> both the users mailbox and the autoresponder transport.

Well if this autoresponder is designed to respond to e-mails sent to
humans then why not use procmail or vacation to do the same thing?

> The
> autoresponder can then look up the user in whatever backend it uses to
> decide whether a response is necessary or not.  The autoresponder does
> not speak to the Big Bad Internet (tm) only to designated MTA(s).  It
> then passes back any response email to the MTA for processing and the
> MTA is free to accept or reject that email depending on configuration.

Sending e-mails in php is easy, the mail() (http://uk.php.net/function.mail)
function has been available since PHP3.  So if I set up a pipe from the MTA to
my PHP3 program then I could do the same thing.
 
> Just because a system wants to speak SMTP doesn't mean it has to be a
> fully fledged mail server. This particular use of the SMTP class is not
> intended to implement an MTA, only to look like an MTA.  It does not
> have the facility to pass email on to anywhere - it just stores the
> mail on disk.

This is true, but most people say that if it looks like a duck and it
quaks like a duck it will get treated like a duck.  So some are going
to assume that it can be used in very way a duck can.

> > This worries me.  Have you written a SPAM remailer here?  If any email
> > sender can connect from anywhere then haven't you created a way for
> > spammers to spread their evil seeds?
> <snip>
> 
> No because, again, its not an MTA, it only looks like an MTA.  As
> mentioned above and evil seeds notwithstanding, this particular project
> has no facility to do anything with email it receives apart from store
> it on disk.  Neither does it speak client side SMTP.  It only has the
> facility to receive mail and dump it to a file, exposing the SMTP
> transaction.  Not sure if you read the project page fully, or maybe it
> doesn't say what I think it says! 

Hang on, hang on.  You said that this is an autoresponder.  Autoresponders
send e-mails, THIS IS HOW THEY RESPOND.  Is your system just sending 
bounce replies?  To send an email the system must "speak client side
SMTP" or, to put it another way, "sender side SMTP".
 
> <snip>
> > Also what do you do with email for postmaster@<local-machine> (and if
> > you're running a web server webmaster@<local-machine>)?  The RFCs for
> > e-mail processing *require* that you accept all mail for postmaster,
> > even spam, as mostly this is used to report problems with e-mail
> > configuration.
> <snip>
> 
> I know the RFCs require functional system addresses but.... this is not
> an MTA! It is not intended for use as an MTA and never will be.  No
> domain will ever terminate at this software, simply because it does not
> have the facilities to deal with incoming email, apart from to store it
> on disk.

I would say that *any* email that is (incorrectly) routed via you system
*will* *end* because all your system does is store it to disk - regarless
if it is for that machine or not.

> It is not intended and cannot receive email destined for
> someone's mailbox and it never will do that.  The tcp streams
> implementation is sequential, not concurrent, meaning that it is of
> little use if more than one client is using it.  This is a 'feature'.
> As a test server, that's all it needs.

I don't understand what you're saying here.  If the TCP stream in PHP5
is sequenctial that may just mean that a second connection will block 
until the one currently being processed has completed.
 
> In the case of an autoresponder using the base SMTP class, its up to the
> software to have some intelligence about the envelope email address and
> mail headers. For example, a decent autoresponder won't respond to
> mailing list addresses.

Very true.

> There is no reason for such software not to
> respond to a postmaster@ or webmaster@ address.

True, but those two email address should resolve to a mailbox read by
a human, probably the mail and web admin staff.

> Likewise it would not
> block email from reaching those addresses as local recipients, because
> that is not its function and it has no ability to access the local
> mailboxes - that's the MTA's job.

But an MTA that has handed over the email message to your system *has*
passed on the responsability of delivering that e-mail to your system.
That is implessit in the SMTP protocol.  If the original sender didn't
take a copy of that e-mail when it was first sent then your copy may
be the *only* copy in the universe.
 
> I don't think you're grasping what the project is or
> does.

You're right - unless it was to teach you how to use sockets in PHP.

> I am not building a PHP MTA, the main goal of the project is
> to write a server side SMTP interface in PHP.  That does not constitute
> anything different from the interfaces available in Perl, Ruby, C, etc.

Well the only interfaces/libraries I'm aware of there are senders of
e-mail, those are clients.
 
> The idea behind it is threefold:-
> 
> 1. Create a PHP class that can speak server side SMTP.

Which is used only to receive e-mails.
 
> 2. Use the above class to create a test server that can receive email
> and dump it to a file that exposes the SMTP session, for use in
> testing.  This project is mainly intended to test the functionality of
> the SMTP class built in point 1.

As a development step this is fine.
 
> 3. Implement an autoresponder system that uses the above SMTP class as
> its interface to the MTA.

At which point you are sending e-mails back out.
 
> Hope that is now clearer.

Not at all.

> I'll tweak the project page to explain the
> purpose more fully.

The purpose of the autoresponder would be a start.  It it a vacation like
program telling senders that the user is out of the office today because
of holiday, bank holidays or sickness?

Or is it an autoreponder for doing remote processing (like mailman) with
out a human operator being involved?

Steve
-- 
Paranoid Club meeting this Friday.  Now ... just try to find out where!
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