ANNOUNCE - qmail-smtpd Plugins for MAIl, RCPT, DATA Phase

[Manvendra Bhangui]

I am writing (actually finished writing) a method by which we can write

plugins for qmail-smtpd. The plugins will allow us to execute our own

functions in smtp_mail(), smtp_rcpt() and smtp_data() in qmail-smtpd. By

using plugins we will be able to alter the behaviour of the MAIL, RCPT,

DATA phase of a SMTP session.

The way it works qmail-smtpd scans for all shared objects with names

(smtpd-plugin0.so, smtpd-plugin1.so, ... and so on) in the directory

/var/qmail/plugins. The function dlopen() is called on all the shared

objects. A function plugin_init() is called to initialize a PLUGIN

structure defined in plugin_init.h The PLUGIN structre contains pointers

to funcations to be executed in smtp_mail(), smtp_rcpt() and smtp_data()

in qmail-smtpd. These functions are passed arguments like mailfrom, rcptto,

localip, tcpremoteip, etc

We can terminate the MAIL, RCPT, DATA session by returning non-zero

integer in the function written as part of the plugin. We can also

define the message to be returned to the user by simply defining a variable

named 'mesg' inside these functions.

To write a plugin is very simple. We just need to write the functions

from_plug(), rcpt_plug() or data_plug(). It is upto to us to write all

the three functions or write any one of them. e.g.

In case we do not want to do anything in the RCPT session, then we can

just return 0 in the function rcpt_plug() and our rcpt_plug() function can

be

int

rcpt_plug(char *remoteip, char *from)

{

        return (0);

}

A template for writing plugins is included in the patch. The template is

smtp_plugin.c. To compile the plugin we just need to do the following

gcc -Wall -O4 -fPIC -c smtp_plugin.c

gcc -shared -rdynamic -nostartfiles -fPIC -s -O4 -o smtpd-plugin.so smtp_plugin.o

Just copy the file smtpd-plugin.so to /var/qmail/plugins directory

Examples of plugins could be writing badmailfrom, badrcptto as a plugin. I am sure

you will be able to visualize more than what I can do at the moment.

You can download the patch at

http://sourceforge.net/projects/indimail/files/netqmail-addons/smtp_plugins/

The code is free and without any warranty. If you notice any mistake in the code

let me know so that I can fix it.

--
Regards Manvendra - http://www.indimail.org

[John Levine]

>I am writing (actually finished writing) a method by which we can write
>plugins for qmail-smtpd. The plugins will allow us to execute our own
>functions in smtp_mail(), smtp_rcpt() and smtp_data() in qmail-smtpd. By
>using plugins we will be able to alter the behaviour of the MAIL, RCPT,

>DATA phase of a SMTP session. ...

This is a fine idea. But why don't you use Bruce Guenter's mailfront
package, which is well debugged, already has a useful set of plugins,
and interfaces very nicely with qmail?

If you also use his CVM package, it can check at SMTP time whether
there's a .qmail file for an address, so in most cases you can reject
rather than bounce undeliverable mail.

Regards,
John Levine, jo...@iecc.com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. http://jl.ly

--
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Please direct questions, flames, donations, etc. to news-...@muc.de

[Manvendra Bhangui]

On Sun, Apr 17, 2011 at 9:52 PM, John Levine <jo...@iecc.com> wrote:

This is a fine idea.  But why don't you use Bruce Guenter's mailfront
package, which is well debugged, already has a useful set of plugins,
and interfaces very nicely with qmail?

If you also use his CVM package, it can check at SMTP time whether
there's a .qmail file for an address, so in most cases you can reject
rather than bounce undeliverable mail.

Thanks for pointing out this. I was unaware of the CVM package. It looks interesting and I will take a look at this.