Snert . Com - Software - A Mail Server/1.2

A Mail Server/1.2
from Snert . Com

Liam Den Son >|< Nos End Mail

Description

This is a small, simple, modular dial-on-demand mail server that can be used within the Cygwin environment for Windows. This mail server, could in principle, work under any Unix variant (though not tested), since the design uses Unix-based tools and ideas.

This project came into existence for several reasons, the most notable is that a large motor yacht required a replacement for their 3rd party Windows based mail server solution that was used by the owner, ship's captain, and crew. The Windows solution was proving to be too complicated to administer with multiple access providers world-wide and their three means of connectivity: land-line, GSM, and SatCom.

Replacing the Windows 2000 server with a Linux box was not an option, since it provided other services to the yacht. Alternative 3rd party Windows based mail solutions were researched, but appeared to be no better than the existing solution. A Unix-like solution that could be built in a hurry seemed like an idea to try and the Cygwin environment provided a good basis from which to start. However, most of the popular Unix mail solutions such as Sendmail, Postfix, Qmail, Exim, and the Courier Mail Server have not been ported to the Cygwin environment and would probably take more time port than was available. This meant either finding or writing the necessary pieces for a solution.

A solution would entail several identifiable pieces: a dialler, a basic SMTP server, a complete POP3 server, a mail transport agent, and a scripting language to bring all the pieces together.

The solution outlined here has a simple modular design that uses existing software tools from a variety of sources: the Cygwin environment provides most of the framework and "glue" with scripting tools like Bash, Perl, Python, or Ruby being readily available; Windows 2000's rasdial, which is suitable for use in scripts, solves the dialler problem (thankfully); a modified fetchmail for a mail transport agent; Cygwin provides an inetd super-server, that can run as a Windows 2000 service, combined with small smtpd & pop3d inetd servers which provide a mail queue and local mail delivery & retrieval facilities.

The smtpd server supports RFC 2821 & 2882 and the pop3d server supports RFC 1939, 1957 & 2449. Both the smtpd and pop3d work fine with fetchmail and popular mail clients such as Netscape, Mozilla, Opera, and Outlook Express. The smtpd and pop3d share a common configuration file, mail.cfg, that can be managed with mailcfg.pl. Both servers implement mail boxes similar to, but not entirely the same as, maildirs as developed and used by Qmail and the Courier Mail Server. The outbound mail queue is itself a mail drop box that can be accessed by the modified fetchmail via the pop3d server, so as to forward mail to an upstream SMTP server. The simple modifications to fetchmail removed the burden of having to write a full smtpd gateway and shortened development time. The diagram above shows the logical structure and data flow of the principal interacting pieces.

I've recently had some feedback from Ricardo d'Angelo at astrazeneca dot com who explained to me how he intends to use A Mail Server. His firm has a web application for their sales representatives to help organise promotional events, which also involves an approval workflow mechanism. Ricardo writes:

We designed the training in such a way that the different roles are appropriately played to create a realistic environment. As our trainer needs to travel across the country we implemented a network of laptops with wireless adapters, and the only piece that was missing was to mimic the mail server, to implement the notification piece that is an essential part of the application.

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Build

The setting up of a build environment can be a time consuming process and requires some understanding of Unix, which the Cygwin environment emulates by providing the necessary APIs and ported tools. My development environment already existed for assorted other projects prior to this one and so I will NOT provide support, help, explanations, tips, tricks, etc. on how to setup Cygwin for the purpose of building my software for this project. However, I can tell you that you will require the following:

ygwin: To deploy A Mail Server, you'll require the Cygwin base install including binutils, inetutils, less, and perl at a minimum. The Cygwin supplied version of fetchmail is of no use. To build A Mail Server binaries for smtpd, pop3d, and fetchmail from scratch, you'll also require a build environment with bison or yacc, flex, gcc, make, openssl libraries & development headers, and patch all from the Cygwin distribution.
: To build the modified fetchmail binary, you'll require the fetchmail-5.9.13 source distribution. You'll need to apply the fetchmail-5.9.13.patch included with my source distribution and build fetchmail with SSL support. My patch has been submitted to the author of fetchmail and may appear in a future release (I hope). Please read the fetchmail INSTALL document on how to configure and build the binary.
LibSnert: To build A Mail Server binaries for smtpd and pop3d, you'll have to build my development support library to link with.

Deploy

Having just recently deployed A Mail Server solution on a motor yacht, the following documents those steps involved.

Login to Windows 2000 Pro as the Administrator. Note that Windows XP Pro should work, though the location of things may have changed (unknown); Windows XP Home Edition is a cripple and not recommended for anything.
Install the base Cygwin environment and make sure to include binutils, cygrunsrv, inetutils, less, and perl packages.
On Windows 2000, you need to update the system wide environment variables found via:
Control Panel
  > System
    > Advanced
      > Environment Variables
1. Add the variable: CYGWIN=ntsec
2. Prefix the PATH variable with: c:\cygwin\bin;
Also for Windows 2000, in order for the inetd service to run correctly you'll need to modify the Local Security Policy found via:
Control Panel
  > Administrative Tools
    > Local Security Policy
      > Local Policies
        > User Rights Assignment
For each of the following, add the Administrators group to the list of names:
1. Act as part of operating system
2. Increase quotas
3. Logon as service
4. Replace process level token
Note that Windows XP Home Edition does NOT support the ability to change Local Security Policy in this manner, if at all.
Modify the properties of the Cygwin shortcut so that the Target field says this:
C:\cygwin\bin\bash.exe --login -i
Now using the modified Cygwin shortcut, open the Cygwin shell window and unpack the archive downloaded from this web site. You might want to view the manifest.txt to see where files will be unpacked relative to the Cygwin root directory.

$ tar -C c:/cygwin/ -xzpvf ams102.tgz
The inetutils package from Cygwin does not provide a traditional services file. It is unclear whether this file is required or not with the Cygwin version of inetd. A sample has been provided and should be renamed if required:

$ mv /etc/services.sample /etc/services
Next the file /etc/inetd.conf should either be replaced with the sample /etc/inetd.conf.sample or the following two lines added to the existing one:

smtp stream tcp nowait Administrator /cygdrive/c/cygwin/usr/local/sbin/smtpd smtpd pop3 stream tcp nowait Administrator /cygdrive/c/cygwin/usr/local/sbin/pop3d pop3d
Enter the following two commands to install and start the inetd service under Windows 2000:
$ cygrunsrv -I inetd -d 'Cygwin Inetd' -p /usr/sbin/inetd -a '-d' -e CYGWIN="tty ntsec"
$ cygrunsrv -S inetd
Use the following script to help you configure your mail server accounts:

$ /usr/local/sbin/mailcfg.pl
Use the following script to help you configure your mail transport for incoming and outgoing email with a remote mail server:

$ /usr/local/sbin/mailtransportcfg.pl
Configure and test any new Dial-Up Networking entries. The mailcheck.pl script then needs to be configured for each entry you intend to use. The simplest way to do this is using the following configure script:

$ /usr/local/sbin/mailcheckcfg.pl

Please note that the "Show terminal window" option for Dial-Up Networking connections must NOT be on, otherwise the mailcheck.pl script will fail.
Rather than go to the trouble to setup Cygwin cron, use the Windows 2000 Scheduler to invoke the following script on a schedule of your choosing:

c:\cygwin\bin\perl.exe c:\cygwin\usr\local\bin\mailcheck.pl
Done. Of course, test the system to see that mail clients can send & receive email, that mail gets delievered to local mail boxes and/or queued in the outbound mail box. Then test that mail is sent to and received from the remote server. Send mail from a remote account to the local system, reply to this email to see if it makes the round trip successfully.

Note that the set up of mail client software is outside the scope of this document, but in general a mail client, such as Mozilla, Opera, or Outlook Express, will require the IP address of the incoming POP3 server and the outgoing SMTP server, a user mail box name and a password. Since the POP3 and SMTP server here are on the same machine, the values entered should be the same.

Administration

The hardest part of this mail server is the setup & security. Once that is completed, maintaining the system is simply a matter of using one or more of the following configure scripts:

/usr/local/sbin/mailcfg.pl [cfg-file]: Used to specify local domains names accepted by the server, define user mail boxes & their passwords, define email address mappings to mail boxes, and miscellaneous options.
/usr/local/sbin/mailtransportcfg.pl (not yet written): Defines the mail transport accounts. This is by far the most complex task.
/usr/local/sbin/mailcheckcfg.pl: In the case of a mobile system, such as on a motor yacht, this script allows you to manage dial-up connections, their associated user name & passwords, and to select which one to use at any one time.

Liam Den Son >|< Nos End Mail

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