Sendmail-Address-Rewrite(1).pdf

sendmail address rewriting mini−HOWTO

Table of Contents

sendmail address rewriting mini−HOWTO. ....................................................................................................1

Thomas Roessler, roessler@guug.de. ......................................................................................................1

1. Introduction. .........................................................................................................................................1

2. File Roadmap. ......................................................................................................................................1

3. Configuring sendmail ..........................................................................................................................1

4. Further reading. ....................................................................................................................................1

1. Introduction. .........................................................................................................................................1

2. File Roadmap. ......................................................................................................................................2

3. Configuring sendmail ..........................................................................................................................2

3.1 The main configuration file. ..............................................................................................................2

3.2 Address rewriting. ..............................................................................................................................3

3.3 Aliases. ...............................................................................................................................................4

4. Further reading. ....................................................................................................................................5

sendmail address rewriting mini−HOWTO

Thomas Roessler, roessler@guug.de

v0.0, 6 May 1998

This document is a brief description of how to set up sendmail's configuration file for the home user's

dial−up access.

1. Introduction

2. File Roadmap

3. Configuring sendmail

· 3.2 Address rewriting

3.1 The main configuration file

· 3.3 Aliases

4. Further reading

1. Introduction

We assume that you have the kind of Internet access which seems to be most common at universities and

online services nowadays: You dial into your provider's network using PPP over a serial connection. Your

incoming mail is spooled at the provider's POP or IMAP server, while outgoing messages are to be sent via

SMTP. You don't have a domain name of your own, so everything has to use one address.

We assume that you have already installed a fairly recent version of Eric Allman's sendmail (version 8.8.8 is

current at the time of this writing and should work fine).

This document is partially referring to specific properties of Debian GNU/Linux systems; users of different

distributions will have to take some care.

Make sure you have the following information at hand:

· Your Internet mail address

Your ISP's mail server

The configuration we are planning has two main goals:

Sending mail between various local users must be possible.

The outside world must see the local users' ISP mail addresses, not the local ones.

sendmail address rewriting mini−HOWTO

sendmail address rewriting mini−HOWTO

To achieve this, we will make use of sendmail's genericstable feature.

2. File Roadmap

We will put all of sendmail's configuration files in a separate directory under etc : etcmail . Usually,

sendmail will expect these files to reside directly under etc . To avoid problems, etcsendmail.cf should

be a symbolic link to etcmailsendmail.cf .

The following files will populate etcmail :

· aliases − contains additional local addresses

=20

· genericsdomain − contains some information on your local host's configuration

· genericstable − contains the actual rewriting rules.

· sendmail.cf − sendmail's configuration file

· sendmail.mc − the source of sendmail.cf .

Some of these files will be accompanied by .db files. They contain hashed databases for sendmail's direct

use.

We assume that the cf part of sendmail's source tree resides under a directory named

usrlibsendmail.cf . This is the case on Debian GNU/Linux systems. Other distributions will put this

stuff at different places. Please refer to your distribution's documentation for details.

3. Configuring sendmail

3.1 The main configuration file

Sendmail uses a highly complex rule system for it's configuration. While you can do lots of neat tricks with

this stuff, writing a sendmail.cf file from scratch is rather unusual and time−consuming. If you are

interested in doing so, you should stop reading this document right now and instead read the "Bat Book" from

O'Reilly.

Instead of hand−crafting these rules, we will rely on the m4 macro processor to put together our configuration

file from ready−made pieces which are distributed together with sendmail.

Let's look at the first lines of the sendmail.mc file:

include(/usr/lib/sendmail.cf/m4/cf.m4)

VERSIONID(`sendmail.mc − roessler@guug.de')

OSTYPE(debian)

define(`ALIAS_FILE',`/etc/mail/aliases')

In the beginning, cf.m4 is included. This m4 macro file contains lots of macro definitions for the rest of the

file. Be sure that the path you give here is correct − the one we are representing in our example is typical for

2. File Roadmap

sendmail address rewriting mini−HOWTO

Debian GNU/Linux. The OSTYPE macro is used to give some useful defaults for certain configuration

values. If you aren't using a Debian system, you should replace the word "debian" by "linux" here.

ALIAS_FILE tells sendmail where to look for the list of aliases.

The following lines tell sendmail to use the genericstable feature, and where to find the configuration

files needed to use it:

FEATURE(masquerade_envelope) FEATURE(genericstable, `hash

−o /etc/mail/genericstable')

GENERICS_DOMAIN_FILE(`/etc/mail/genericsdomain')

The masquerade_envelope feature tells sendmail to apply header rewriting to the envelope sender of a

message. This is the mail address to which external mail delivery subsystems will direct their delivery failure

reports and warning messages. The generics* files will be explained below.

Now, we have to define a so−called smart host, that is, a machine which will handle outgoing mail for your

system. Note that this machine may be different from your ISP's POP and IMAP servers. If in doubt, contact

the hotline. The code in the master configuration file:

define(`SMART_HOST',`mail−out.your.provider')

Please replace mail−out.your.provider by the fully qualified hostname of your internet service provider.

The final two lines include the "mailer" definitions which are needed by sendmail to find out how to handle

various types of mail:

MAILER(local)

MAILER(smtp)

To generate the sendmail.cf file from this sendmail.mc , type the following commands (as root):

# m4 sendmail.mc > _sendmail.cf

# mv −f _sendmail.cf sendmail.cf

Note the technique of writing m4 's output to a temporary file which is thereafter moved to the proper place.

This helps us to prevent sendmail from reading partially written configuration files.

3.2 Address rewriting

First, we have to tell sendmail what addresses are to be considered local (and thus should be subjected to the

rewriting). This is quite simple: Just put the fully qualified host name of your machine into the file

etcmailgenericsdomain . To get your host's fully qualified name, type the following command:

3.2 Address rewriting

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: