Version ID: $Id: dialup.html,v 0.5 2004/03/27 16:15:25 emma Exp $

Preface

This documentation bears information on how to solve some common Postfix setup problems. After it has stabilized, I will offer it for inclusion into Postfix.

Limiting the impact of errors

Back-up your configuration and mail directories before changing anything so as to be able to quickly revert to your configuration in case the modified fails.

Consider using RCS or CVS (or other revision control systems) to keep old versions of your configuration files.

About Postfix

Postfix is a stable, fast and secure Mail Transfer Agent for Unix. It is developed by Wietse Venema for IBM and freely available.

Current status of this document

This document is currently still incomplete and under development, this, it may change often. I really appreciate feedback, be it that you have success with older versions, that it does not work for you or whatever else. See the end of this document for my mail address.

Special configurations with Postfix

General assumptions

Being up-to-date

Note this document assumes you are running a Postfix version no older than 20010228-pl05. Type /usr/sbin/postconf mail_version to find out.

Adjust paths

The paths to configuration files and programs shown below are quite common, but may differ from your setup. It is expected you adjust the paths according to your setup.

Adjust data base types

Depending on your system software, you need to adjust your configuration maps, usually hash vs. dbm. See postmap(8) for details.

Running Postfix on Dial-Up LANs, retaining immediate SMTP delivery for your LAN

It is expected that Postfix works properly while you are online.

Problem

Imagine you have a small LAN set up with an intermittent (dial-up) Internet link. You want your external mail be sent out only when you are online, but local mail be sent immedately via SMTP. (This documentation does not apply if your Postfix mail server is to catch and locally deliver all your mail).

What you should read before reading on here

Documentation you are expected to have read through:

html/rate.html: Always postponing delivery
html/faq.html: Running Postfix inside an intranet
html/faq.html: Running Postfix on a dialup machine
html/faq.html: Delivering some users locally while sending mail as user@domain

Answer

Lines in bold are file names which need to be modified according to succeeding lines.

Configure Postfix as if running in an intranet. See the original Postfix FAQ for details.
Define a hold service for outbound mail (mail that leaves your LAN). See the "Always postponing delivery" section of the Postfix documentation for details.
```
    /etc/postfix/master.cf
    hold     unix - - - - - smtp
       
```

Tell Postfix that your default transport is hold and that it is always to be deferred:

    /etc/postfix/main.cf
    default_transport=hold
    defer_transports=hold

Tell Postfix you want to use transport maps...
```
    /etc/postfix/main.cf
    transport_maps = XXXX:/etc/postfix/transport
```
IMPORTANT: replace XXXX by your default map type, usually hash (if your system has db) or dbm. FIXME: figure if regexp or pcre maps are legal here
...then write that map:
In that file, list your local machines or your domain like this, replacing your actual host/domain names.
```
    /etc/postfix/transport
    thishost.my.domain             local:
    localhost.my.domain            local:
    .my.domain                     smtp:
    another.host.in.my.lan         smtp:
    yet.another.host.without.dns   smtp:[10.11.12.13]
```
See the Intranet section in the FAQ and the transport(5) for details on the configuration file format. Do not omit the local: entries or you will not be able to receive mail. See the FAQ.
Tell Postfix to convert that text file into a data base, replacing the XXXX by the map type you used in the configuration file. (Do this every time you change the transport file!) As root, run
```
    postmap XXXX:/etc/postfix/transport
```

MANDATORY: Every time your machine goes online, do

        /etc/ppp/ip-up
        /usr/sbin/postfix flush

OPTION: Have Postfix deliver external mail immediately as long as you are online:
(replace your proper paths)

    /etc/ppp/ip-up
    /usr/sbin/postconf -e defer_transports=
    /usr/sbin/postfix reload

    /etc/ppp/ip-down
    /usr/sbin/postconf -e defer_transports=hold
    /usr/sbin/postfix reload

OPTION: you are not having DNS in your LAN:
(replace your proper paths)

    /etc/ppp/ip-up
    /usr/sbin/postconf -e disable_dns_lookups=no
    /usr/sbin/postfix reload

    /etc/ppp/ip-down
    /usr/sbin/postconf -e disable_dns_lookups=yes
    /usr/sbin/postfix reload

Of course, you will only need to run postfix reload after the last postconf line in a file, not per each.

References

http://www.postfix.org/ - Postfix' home page, carries online documentation.
http://www.opensource.org/docs/definition_plain.html

Liability and licenses

This document is subject to Federal German and Northrhine-Westphalian laws. Here are the important summaries:

Somebody who gives advise or recommendations to somebody else is not obliged to compensate for damages that arise from following the advise or recommendation. See §675 (2) BGB.
I do not need to claim "copyrights" or reserve my rights, I am keeping the copyright of all my works with or without explicit copyright statements, unauthorized reproduction and the attempt thereof are prohibited either way. See §106 UrhG.

This document may be integrated into Wietse Venema's Postfix project as long as that software conforms to the Open Source Definition.

This document may also be redistributed when unaltered by proxies. Lossless compression with unpatented algorithms and transmission of differences against older versions with unpatented algorithms shall not be considered alteration.

If you have any other needs, let me know and I'll see if I can do something about it.

$Log: dialup.html,v $
Revision 0.5  2004/03/27 16:15:25  emma
Add missing postfix reload, reported by Georg Baum. Thanks!

Revision 0.4  2003/07/08 18:24:57  emma
Remove cruft, update to HTML 4.01 + CSS.

Revision 0.3  2002/02/19 15:40:33  emma
Mark postfix flush/sendmail -q as mandatory.

Revision 0.2  2001/10/03 11:30:38  emma
Fix link to OpenSource definition. Mention 20010228-pl05 as required version,
because 19991231 is unmaintained.

Matthias Andree