Spam (junk email) filtering in Debian GNU/Linux

Chris Lale

       chrislale@users.sourceforge.net

      

Revision History
Revision 0.123 January 2004Revised by: cl
Initial release

This document describes how to deal with spam on a typical home computer with a dialup (ppp) Internet connection. It focuses on using evolution as an email client. evolution is a graphical groupware suite which includes good email client with filtering abilities. The setup described in this document is known to work with Debian GNU/Linux 3.0 (Woody) versions of evolution (1.0.5-1), mail (8.1.2), exim (3.35-1), fetchmail (5.9.11-6), procmail (3.22-5) and spamassassin (2.20-1woody).

Table of Contents
1. Introduction
1.1. What is spam?
1.2. What can you do about spam?
1.3. Email software components
1.4. Mail on a Debian system
1.5. Outline of the installation
1.6. Information you need before you start
1.7. Names used in this document
2. evolution- email client providing the mail user agent (MUA)
2.1. About evolution
2.2. Install evolution
2.3. evolution's 'Inbox' folder
2.4. Configure evolution to send mail to and retrieve mail from a remote server
2.5. Test evolution's configuration
3. eximand procmail
3.1. About exim - mail transport agent
3.2. About procmail - mail delivery agent
3.3. Local mail
3.4. .forward file
4. fetchmail - mail-retrieval and forwarding utility
4.1. About fetchmail
4.2. Install fetchmail
4.3. Configure fetchmail
4.4. Test fetchmail
5. fetchmaildaemon - run fetchmail in the background
5.1. About the fetchmail daemon
5.2. How to invoke the fetchmail daemon
5.3. Configure the fetchmail daemon
6. spamassassin
6.1. About spamassassin
6.2. procmailand spamassassin
6.3. Local mail
6.4. Putting it all together
7. What next?
A. Appendix: About this document
A.1. Copyright information
A.2. Latest version
A.3. Bugs, errors and mistakes
A.4. Spelling, punctuation and grammar
A.5. Conventions used in this document
A.6. Bibliography

1. Introduction

1.1. What is spam?

Spam is junk email. You may come across other synonyms for spam including UCE (Unsolicited Commercial Email) and UBE (Unsolicited Bulk Email).

To spam is to mass-mail unrequested identical or nearly-identical email messages, particularly those containing advertising. Especially used when the mail addresses have been culled from network traffic or databases without the consent of the recipients (see the Linux Dictionary).

Firewalls do not protect you against spam, but you can use other software to identify and filter out junk email.

1.2. What can you do about spam?

One thing everyone can do is to be careful when sending email to multiple addresses. Use Bcc: (blind carbon copy) to send to a message to multiple addresses, and leave the To: and Cc: fields empty. This means that none of the recipients gets any of the other of the other addresses. The addresses are less likely to be picked up by potential spammers .

If your ISP (Internet Service Provider) or web hosting provider has the facility to filter out spam, use it. It save you wasting time and money downloading rubbish.

If your provider does not filter email, or if you still have some spam coming through your provider's filter, read on. This document explains how to set up email filtering on your own home computer.

1.3. Email software components

1.3.1. Incoming mail

The type of software that manages email on your computer falls into three loosely defined catagories: Mail Transport Agent, Mail Delivery Agent and Mail User Agent. There is an article describing generic mail flow. These mail agents are often incorporated into a single software application (eg evolution, mozilla mail, etc). Figure 1 shows a typical system for receiving email.

Figure 1: the major components of a mail system dealing with incoming mail.

  1. Mail Transport Agent (MTA), sometimes referred to as a Mail Transfer Agent. A mail transport agent is software that enables mail to travel from one mail system to another. Your provider's server uses an MTA to send you your mail. You must have an MTA at your end of the connection. A standard Debian installation uses exim, but you may come across others eg sendmail, smail, qmail, etc. Typically, the MTA passes the mail onto an MDA.

  2. Mail Delivery Agent (MDA), sometimes referred to as a Local Delivery Agent (LDA). A mail delivery agent is software that takes mail from an MTA and passes it on to a mailbox or another MTA. A standard Debian installation uses procmail, although there are others eg deliver.

  3. Mail User Agent (MUA). A mail user agent is the software that enables a user to write, send, receive and read email. A standard Debian installation uses mail for local mail. Other mail user agents include elm, pine, eudora, pegasus, etc.

Mail from your provider normally reaches you using the POP3 protocol. A protocol is a set of rules that govern how things communicate over the network (see theLinux dictionary).

1.3.2. Outgoing mail

Outgoing mail is sent to your provider's server, usually using the SMTP protocol. You use a mail user agent to write the message. A mail transport agent takes the message and passes it on to a mail transfer agent. The mail transport agent passes the message to a mail transport agent on your provider's server (see figure 2).

Figure 2: the major components of a mail system dealing with outgoing mail.

1.4. Mail on a Debian system

1.4.1. Debian local mail

If you have a fairly standard Debian installation, your system is probably set up like this. exim is the MTA and mail is the MUA. mail writes to the mailbox local-user-1@local-host. The contents of the mailbox are stored in the file /var/mail/local-user-1 (sometimes called the spool file). Here local-user-1 is the name that you use to login to your computer.

A user can read the mail using mail as the MUA. The command is: 

mail

The user (local-user-1) can write a mail message to another user (local-user-2) on the system using the command: 

mail local-user-2

1.4.2. Debian external mail

You probably manage your outgoing mail with an email application. This document focuses on evolution, but you may come across others eg links (text-based), lynx (text-based), Mozilla Mail and kmail. These email clients are designed to carry out all the necessary functions (MTA, MDA, and MUA) in one application.

In fact, evolution is not just an email client. It is a graphical groupware suite and also includes a calendar, task manager and contacts database. evolution stores the contents of its email inbox in the user's home directory (˜/evolution/local/Inbox).

1.4.3. Email filter

One reason for concentrating on evolution is that it has good, built-in functions for filtering mail. You can easily set up a filter to place all mail with a particular header into a particular folder. This approach means that you must first add the header to the original message before it reachesevolution. The task of identifying a spam email and adding identifying headers to the message is handled by spamassassin and procmail.

1.4.4. Example of a spam email modified using spamassassin

1.4.4.1. Added headers

The version of spamassassin in Woody is 2.20-1woody. The important header for basic filtering is X-Spam-Flag. It is set to “YES” when spamassassin has identified enough known features of spam messages. 

X-Spam-Status: Yes, hits=5.7 required=5.0
     tests=VIAGRA,BASE64_ENC_TEXT,SUBJ_ALL_CAPS version=2.20
X-Spam-Flag: YES
X-Spam-Level: *****
X-Spam-Checker-Version: SpamAssassin 2.20 
     (devel $Id: spam.html.en,v 1.1 2004/04/30 21:50:38 chrislale Exp $)
X-Spam-Prev-Content-Type: text/plain
X-Spam-Prev-Content-Transfer-Encoding: base64
X-Evolution-Source: mbox:/var/mail/local-user
1.4.4.2. Modified subject line

spamassassin also modifies the subject line of suspected spam. 

Subject: *****SPAM***** WEEKEND VIAGRA
1.4.4.3. Lines added to the top of the message

spamassassin 2.20 adds these lines to the top of the message. (Later versions of spamassassin do this differently.) 

SPAM: -------------------- Start SpamAssassin results ----------------------
SPAM: This mail is probably spam.  The original message has been altered
SPAM: so you can recognise or block similar unwanted mail in future.
SPAM: See http://spamassassin.org/tag/ for more details.
SPAM: 
SPAM: Content analysis details:   (5.7 hits, 5 required)
SPAM: Hit! (2.4 points)  BODY: Plugs Viagra
SPAM: Hit! (1.4 points)  Message text disguised using base-64 encoding
SPAM: Hit! (1.9 points)  Subject is all capitals
SPAM: 
SPAM: -------------------- End of SpamAssassin results ---------------------

1.5. Outline of the installation

There are several stages in the installation process. There are good reasons for this. If you try to install and configure all the software in one go, you are more likely to run into difficulty because there is simply more to go wrong. You may also find it much more difficult to trace faults. By installing and testing in stages, you can go from each stage to the next one with confidence, knowing that your configuration works correctly. Of course, you may need to change one or two configuration settings in the next stage. However, if you make changes one at a time and a fault occurs, you do not have to look very far to find out why.

If you have a dialup connection you probably retrieve external mail from a POP3 server, and send email via an SMPT server. Your Internet Service Provider (ISP) or web hosting provider gave you this information when you set up your account with them. You can also obtain the details you need by looking at the working configuration of a computer that you currently use to connect to your provider. As a last resort you can contact your provider and ask for the information.

1.6. Information you need before you start

You need some detailed information about your ISP (Internet Service Provider) or web hosting provider. If you have printed this document, you may wish to fill in the details in this table.

Information you need

Details of the account with your provider

your provider's telephone number

 

the address of your provider's POP3 server (for your incoming mail)

 

your username for logging in to the POP3 server

 

your password for logging in to the POP3 server

 

the address of your provider's SMTP server (for your outgoing mail)

 

1.7. Names used in this document

The examples in this document use pseudonyms to represent usernames, computer names etc. If you have printed this document, you may wish to use this table to make a note of the real names on your system.

1.7.1. Names used on your (local) computer

Pseudonym

Description

Real name on your system

firstname surname

your full name

 

local-host

the name of your (local) computer. (You can find out by entering hostname at the command prompt

 

local-user or local-user@local-host

your username on the local computer

 

Example

the account name used evolution to identify your provider (eg the provider's name)

 

1.7.2. Names used on your provider's (remote) server

Pseudonym

Description

Real name on your system

remote-user-name

your username on the remote server (isp or hosted server)

 

remote-user-name@example.net

the name of your account on the remote server

 

mail.example.net

the name of the remote POP3 mail server (that your incoming mail comes from)

 

smtp.example.net

the name of the remote SMTP mail server (that your outgoing mail goes to)

 

You will also need your password for the remote server.

2. evolution- email client providing the mail user agent (MUA)

2.1. About evolution

2.1.1. Outgoing mail

You must configure evolution so that it sends all outgoing mail to your provider's SMTP server. Once this is working you do not need to make any further changes to the configuration for outgoing mail. The filtering of outgoing mail is beyond the scope of this document.

2.1.2. Incoming mail

evolutionalso receives incoming mail directly to your provider's server (usually POP3). Figure 3 shows you the major components of evolution or any other system for collecting POP3 email.

Figure 3: the major components of Evolution

The first step is to configure and test evolution so that it sends mail directly to your provider's server, and receives mail directly from it.

Later, you must change evolution's configuration for incoming mail. This is to allow other software applications to take over some of the processing of mail before it reaches evolution.

2.2. Install evolution

You can use use synaptic (X11), aptitude (console) or apt (command line) to install Debian packages. This document only describes the use of apt. It is good practice to work from a normal user account on your computer, and only switch to the root user when it is necessary. The '$' sign indicates the command line prompt for a normal user. The '#' sign indicates the command line prompt for the root user ('superuser').

Login as a normal user. Open a terminal window (eg gnome terminal). Switch user (using su) to the root user. You must enter the password for root. Use apt to install the evolution package. 

$ su
Password: *******
# apt-get install evolution

Exit from root when the installation is complete. 

# exit
$

2.3. evolution's 'Inbox' folder

Run evolution as a normal user. 

$ apt-get install evolution

Open the mail inbox. 

Menu bar
   File
      Go to Folder ...  Go to folder ... dialogue
Go to folder ... dialogue
   Inbox
OK

The inbox is shown as a folder. You can switch between folders easily using the tree display. There is grey bar below the Menu bar and the Button bar. On the left hand side there is a button showing the name of the selected folder (currently 'Inbox'). Click on the Inbox button to reveal the 'Folders' pane. There is a button on the top right hand side of the 'Folders' pane with a with a mapping pin icon. Click on the mapping pin button to keep the 'Folders' pane permanently visible.

2.4. Configure evolution to send mail to and retrieve mail from a remote server

You must tell evolution the names of your provider's POP3 and SMTP servers, and your username and password on these servers. Run evolution and configure it using the Mail Settings dialogue from the Tools menu. 

Menu bar 
   Tools
      Mail Settings ...  
         Add
Mail settings dialogue 
   Accounts tab  
      Add

This brings up the evolution Account Assistant's Mail Configuration dialogue . 

Mail Configuration dialogue
   Click "Next" to begin
   Next

In the Identity dialogue, enter the full name and email address that you use on your provider's server. 

   Identity dialogue
      Required information 
         Full name: firstname surname
         Email address: remote-user-name@example.net
      Next

In the Receiving Email dialogue, enter details of the email server that you receive emails from. (This is usually a POP3 server.) 

Receiving Email dialogue 
   Server Type: POP
   Configuration
      Host: mail.example.net
      Username: remote-user-name
   Authentication
      Authentication Type: Password
      Remember this password
   Next
   Checking for New Mail
      Automatically check for new mail every 10 minute(s)
      Receiving Email dialogue
Next

Enter details of the email server that you send emails to. (This is usually an SMTP server.) 

Sending Email dialogue
   Server Type: SMTP
   Server Configuration
       Host: smtp.example.net
Next

Enter a name for evolution to identify the account. You can choose anything within reason. One approach is to use your provider's name. You might use 'Example' if your email address is 'remote-user-name@example.net'. 

   Account Management dialogue
      Account Information
         Name: Example
         Next
   Done 
Finish

You may have other accounts that you wish to add. You will save yourself some work by waiting until the whole system is set up and working. You can add further accounts at any time in exactly the same way

2.5. Test evolution's configuration

Test evolution's configuration by sending yourself an email. It should travel from your local computer to your provider's server and back into evolution's inbox folder.

Check that you can see the current contents of the Inbox folder. Connect to the Internet using modem lights applet (Gnome) or pon and poff (command line).

Use either the File menu or New Message button to open the Compose a 'message' dialogue. 

Menu bar 
   File
      New  
         Mail Message

or 

Button bar
   New Message

Address the message to yourself. Filling in only the 'To' and 'Subject' fields is sufficient. Then send the message. 

Compose a message dialogue
   To: remote-user-name@example.net
   Subject: Evolution test 1
Send

Give the message a couple of minutes to reach the remote server and to be returned. Retrieve the email by clicking on the 'Send / Receive' button on the Button bar. Of course you may have to wait a little longer. Just repeat the request until the message arrives. 

Button bar
   Send / Receive

Move on to the next section when you are sure that the system is working correctly.

3. eximand procmail

3.1. About exim - mail transport agent

eximis a mail transfer agent (MTA).

The Exim manual describes exim like this. exim “contains facilities for verifying incoming sender and recipient addresses, for refusing mail from specified hosts, networks, or senders, and for controlling mail relaying”. and the Debian Reference. It sounds complicated! This is where Debian comes to the rescue. You install exim from a Debian package (.deb file). exim is probably already configured and working.

The inetd.conf file starts exim running every time you boot your computer (see Exim's README.Debian file).

You may find the newbieDoc article “A simple configuration of Exim” useful.

3.2. About procmail - mail delivery agent

procmail is an enhanced MDA with many extra features. procmail can deliver mail from exim (the configuration is in /etc/exim/exim.conf).

Like exim, procmail is probably already configured and running on a standard Debian installation (see figure 4).

Figure 4: Exim and Procmail collecting local mail

3.3. Local mail

The local mail system is available to all local users (all those who login to your computer). In a standard Debian installation there is always an account for the Root user. There should be at least on other account for a normal user - your account. (You should never use the Root account unless it is absolutely necessary.)

Time for a quick test! You will need a mail user agent (MUA) to send and receive messages. You could use mutt, but mail. To run mail from the command line.

Send yourself a message using mail. Enter a subject and a short message, but do not worry about sending a carbon copy (Cc:). Use the 'enter' key for each new line, and 'control' key + 'd' key to end each section. 

$ mail local-user 
Subject: local message
hello
ctrl-D
Cc:
ctrl-D
$

Now check that the message has reached you local mailbox. Look inside the /var/mail/local-user file using the cat command. 

$ cat /var/mail/local-user
From local-user@local-host Wed Feb 04 12:11:46 2004 
Return-path: <local-user@local-host> 
Envelope-to: local-user@local-host 
Received: from local-user by local-host with local (Exim 3.35 #1 (Debian))
     id 1AoLsg-0000in-00
     for <local-user@local-host>; Wed, 04 Feb 2004 12:11:46 +0000
To: <local-user@local-host> 
Subject: local message 
Message-Id: <E1AoLsg-0000in-00@local-host>
From: local-user <local-user@local-host>
Date: Wed, 04 Feb 2004 12:11:46 +0000
Status: O
hello
$

Read the message using mail. Use the 'enter' key to open the message and enter 'q' to quit. 

$ mail 
Mail version 8.1.2 01/15/2001.  Type ? for help. 
"/var/mail/local-user": 1 message 1 new 
>N  1 local-user@local-host      Wed Feb 04 12:11   14/394   local message 
hello
& q
Saved 1 message in /home/local-user/mbox
$

Mail stores messages in the /home/local-user/mbox file. You can check this too. 

$ cat /home/local-user/mbox

3.4. .forward file

eximis probably already configured to run procmail automatically on your computer. If not, or if you just want to be sure, you can put a hidden file in the root of your home directory which invokes procmail. The file is called .forward. The initial dot means that the file is hidden.

The .forward file has only one line with a pipe character followed by the absolute path to the procmail binary file. 

 |/usr/bin/procmail

Create the file in a text editor and save it as /home/local-user/.forward. The /home/local-user/.forward file invokes procmail automatically as soon as mail arrives.

The /home/local-user/.forward file must be world readable. To be sure, change the permissions to 0644. 

$ chmod -v 0644 /home/local-user/.forward
mode of `/home/local-user/.forward' changed to 0644 (rw-r--r--)

4. fetchmail - mail-retrieval and forwarding utility

4.1. About fetchmail

In a previous section on configuring Evolution to send and retrieve mail, you configured evolution to receive mail from directly from your provider's server. The next step is to get a different application (fetchmail) to do the job instead! There is a good reason for this. You must examine each message for spam before it reaches evolution. fetchmail will collect the mail and forward it to the local mailbox (/var/mail/local-user). exim, procmail and spamassassin will deal with spam on the way to the mail box (see figure 5). You may find the newbieDoc article “Fetchmail configuration” useful.

Don't worry about spamassassin yet - get fetchmail working first.

Figure 5: Fetchmail delivers incoming remote mail into the local mail system.

fetchmailretrieves the mail from your provider's server and forwards it to your local email folder (see figure 5). If you logged into your computer as local-user, fetchmail will place it in /var/mail/local-user. This means that you must reconfigure evolution to retrieve the mail from /var/mail/local-user instead of directly from the remote POP3 account. This is so that the mail can be processed before evolution receives it.

4.2. Install fetchmail

In a terminal window, switch user (using su) to root. Use synaptic (X11), aptitude (console) or apt (command line) to install fetchmail, fetchmail-common and fetchmailconf. 

$ su
Password: *******
# synaptic 
or 
# aptitude
or 
# apt-get install fetchmail fetchmail-common fetchmailconf

Exit from root. 

# exit
$

You must make the following configuration choices during installation:

Read the warnings and locations of related documentation 

OK

Read the information related to the installation of a system-wide fetchmail daemon 

Install a system-wide fetchmail service? Yes

Read the information about running a system-wide fetchmail daemon as either as root or as an unprivileged user 'fetchmail'. 

Run system-wide fetchmail as root? No

Read the warning that a new /etc/default/fetchmail file may override your settings in /etc/fetchmailrc. You will not have any settings unless you have installed fetchmail before! (I checked during my install - /etc/default/fetchmail did not exist.) 

OK

4.3. Configure fetchmail

fetchmaillooks for its configuration details in a hidden file in the current local user's home directory (/home/local-user/.fetchmailrc). It is possible to create this file with a text editor. However, there is a configuration tool (fetchmailconf) that makes building the configuration less prone to typos and other mistakes.

Invoke fetchmailconf from the command line as a normal user. It runs as an X11 application. 

$ fetchmailconf

Choose 'Configure fetchmail'. 

fetchmail launcher dialogue
   Configure fetchmail

Choose the 'Novice Configuration'. 

fetchmail configurator dialogue
   Novice Configuration

fetchmailwill repeatedly check the remote mail server for new mail. The time between each repeat is called the poll interval. A short interval (between 10 and 30 seconds) is useful for testing - you do not want to spend hours staring at you modem lights! You may wish to change this value in a permanent set up to something like 300 seconds (5 minutes). Set the poll interval and the remote mail server's name. 

fetchmail novice configurator dialogue
   Fetchmail Run Controls 
      Poll interval: 30 (seconds) 
   Remote Mail Server Configurations 
      New Server:  mail.example.net

Either double-click or press the <Enter > key.

Enter the protocol of the remote mail server and the user name you use to log into it. 

Fetchmail host mail.example.net dialogue
   Protocol 
      POP3
   User entries for mail.example.net
      New user: remote-user-name

Either double-click or press the <Enter> key

Enter your password on the remote server. 

Fetchmail user remote-user-name querying mail.example.net dialogue
   Authentication
      Password: *******

Enter the username you use to log into the local host (your computer). 

   Local names
      New name: local-user

Delete remote-user-name since there is no such local user. 

      remote-user-name delete

Save and exit in reverse order. 

Fetchmail user remote-user-name querying mail.example.net dialogue
   OK

Fetchmail host mail.example.net dialogue
   OK

fetchmail configurator dialogue
   Save

fetchmail launcher
   Quit

Check the result by looking in ˜/.fetchmailrc. The last line should look like this: 

poll mail.example.net with protocol POP3 user 'remote-user-name' there with password '*******' is 'local-user' here

Notice that the password is not secure. It is saved in an ordinary user's file. Later on you will move the configuration statement to a safer location.

4.4. Test fetchmail

NoteCollect your email before testing
 

It is wise to download all your email before going on. Using your existing email client software. It is possible that some email may be lost during testing if something goes wrong.

It is time to send yourself another email. Compose it in and send it from evolution as before. (See the section on testing Evolution's configuration.) fetchmail should receive it a little while later and forward it to your local-user's local mailbox /var/mail/local-user. You can check this by looking in /var/mail/local-user or by using the mail command at the command prompt. (See the section on local mail.)

4.4.1. Test fetchmail without a ppp connection to the remote server

First, run ˜/fetchmailconf without a ppp connection. This will help you to recognise when an error has occurred. Make sure that there is no ppp connection to the remote server, then invoke ˜/fetchmailconf from the command prompt. It will use the values you put into your ˜/fetchmailconf file. 

$ fetchmailconf
    
fetchmail launcher dialogue
   Test fetchmail

The fetchmail launcher dialogue opens a 'fetchmail run window' so that you can monitor the process. 

fetchmail run window
   Running fetchmail -d0 -v --nosyslog
      fetchmail:  5.9.11 querying mail.example.net (protocol POP3) ...
      ...
      fetchmail: couldn't find canonical DNS name of mail.example.net
      ...
      fetchmail: normal termination, status 11
      Done.
Exit

4.4.2. Connect to the remote mail server and re-test fetchmail

Connect to the remote server using Modem Lights applet (Gnome) or pon and poff (command line). Re-run the test. You may need to repeat the test a few times until the remote server responds. 

fetchmail launcher dialogue
   Test fetchmail

(Repeat as necessary.)

This is what you get when everything is working properly but you have no mail to collect. 

fetchmail run window 
   Running fetchmail -d0 -v --nosyslog
      fetchmail:  5.9.11 querying mail.example.net (protocol POP3) ...
      ...
      fetchmail: POP3< +OK ...
      ...
      No mail for remote-user-name at mail.example.net ...
      ...
      fetchmail: normal termination, status 1
      Done.
Exit

If you do have mail to collect, the 'fetchmail run window' will say so.

4.4.3. Send and receive mail from the remote server

Send yourself (local-user) a message from evolution with the subject 'Fetchmail test1'. You saw how to do this in the section on testing Evolution's configuration.

Run fetchmail to collect the message. 

fetchmail launcher dialogue
   Run fetchmail

The fetchmail launcher dialogue opens a new 'fetchmail run window'. 

fetchmail run window
   Running fetchmail -d0
      ...
      1 message for remote-user-name at mail.example.net (993 octets). 
      reading message remote-user-name at mail.example.net:1 of 1 (993 octets) 
      flushed
      Done.
Exit

fetchmailnot only checks for mail, it also downloads it to your local mailbox and flushes (deletes) it from the remote server.

4.4.4. Check that fetchmail has delivered the test email

Use mail to fetch the message from your local mailbox. Invoke the mail at the command prompt. Read the mail, then type q at the prompt (&) to quit. 

$ mail 
Mail version 8.1.2 01/15/2001.  Type ? for help. 
"/var/mail/local-user": 1 message 1 new 
>N  1 local-user@local-host      Wed Feb 04 12:11   14/394   Fetchmail test 1
& q
$

4.4.5. Configure evolution to retrieve email from the user's local account

NoteLeave evolution's other settings unchanged
 

You only need to change the way evolution receives mail. evolution will continue to send out-going mail directly to the remote SMTP server.

In the section on configuring Evolution, you configured evolution to collect mail directly from the remote mail server. fetchmail does this job now and saves the mail locally in /var/mail/local-user. What you really want is for the email to end up in evolution again. To do this you must reconfigure evolution to retrieve the mail from /var/mail/local-user.

Run evolution. If you have several accounts, temporarily disable all but one account. You can modify the configuration of other accounts, or install new ones, when you have got the whole installation running satisfactorily. 

Menu bar
   Tools  
      Mail Settings ... 
Mail Settings dialogue
   Accounts

Select an account to be disabled and disable it. 

   Disable
OK

(Repeat, if necessary, until only one account is enabled.)

Edit the one remaining account to change the server type from 'POP' to 'Local delivery' from /var/mail/local-user. 

Menu bar
   Tools  
      Mail Settings ... 
Mail Settings dialogue
   Accounts

Make sure that the active account is selected, the edit it. 

      Edit

Change the details for server type. 

Evolution Account Editor dialogue
Receiving Mail tab
   Server Type: Local delivery
   Configuration
      Path: /var/mail/local-user
   OK
Mail Settings dialogue
OK

4.4.6. Test evolution's new configuration

There should still be an email message in /var/mail/local-user. If not, send yourself another local message from the command line. 

$ mail local-user
Subject: test 2
This is a one-line message.
ctrl-D
Cc:
ctrl-D
Cc:  $ 
$

Now fetch the message from /var/mail/local-user using evolution. 

Button bar
   Send / Receive

Look in evolution's Inbox to check that the mail has arrived. 

Menu bar
   File  
      Go to Folder ...  
Go to folder ... dialogue
   Inbox  
     OK

5. fetchmaildaemon - run fetchmail in the background

5.1. About the fetchmail daemon

The fetchmailconf launcher allows you to run fetchmail by clicking on the Run fetchmail button (see the section on sending and receiving from a remote server). This is not very convenient for everyday use. However, you may have noticed that the Run fetchmail button invokes the command fetchmail -d0. The '-d' switch means 'run fetchmail as a daemon'. A daemon is 'a program which runs for an extended period' ... 'in the background, usually unnoticed' (see the the Linux Dictionary). The fetchmail -d command works because you installed the fetchmail daemon when you installed fetchmail as a system-wide service in the section on installing Fetchmail.

5.2. How to invoke the fetchmail daemon

The daemon is controlled by an executable shell script (/etc/init.d/fetchmail). The script runs automatically when you boot into Linux. You can also control call the script manually using the commands /etc/init.d/fetchmail start, /etc/init.d/fetchmail stop and /etc/init.d/fetchmail restart as the root user. The script will not succeed unless it finds a correctly configured /etc/fetchmailrc file. If you try to run it with an incorrect or missing/etc/fetchmailrc you will get an error message. 

# /etc/init.d/fetchmail restart
Restarting mail retrieval agent: system-wide fetchmail not configured.

5.3. Configure the fetchmail daemon

5.3.1. ˜/.fetchmailrc

The ˜/.fetchmailrc file is your personal file produced by fetchmailconf for single user mode. It is ignored by the daemon, but some of the configuration statements must be copied to /etc/fetchmailrc and /etc/default/fetchmail for system-wide daemon mode.

5.3.2. /etc/fetchmailrc

This file is needed if starting or stopping /etc/init.d/fetchmail. It must contain the configuration statement for polling the remote server that fetchmailconf produced . (There is a typo in this file: 'pool' should be spelled 'poll'.) 

poll mail.example.net with protocol POP3 user 'remote-user' there with password '*******'

There is an example statement in the /etc/fetchmailrc created during installation. The example statement ends with a semicolon (;). The semicolon does not seem to be necessary as long as the statement is written all on one line.

Leave the defaults unchanged - only batchlimit is uncommented. 

batchlimit 100

Change owner to user fetchmail and group to root.

WarningSecurity
 

Notice that the password is not encrypted. The /etc/fetchmailrc file must belong to the special user fetchmail, and be readable and writeable only by owner fetchmail. 

# chown --verbose fetchmail:root /etc/fetchmailrc
ownership of `/etc/fetchmailrc' retained as fetchmail:root

Set permissions to read and write only for owner. 

# chmod --verbose 0600 /etc/fetchmailrc
mode of `fetchmailrc' changed to 0600 (rw-------)

5.3.3. /etc/default/fetchmail

The settings in this file override those in /etc/fetchmailrc.

This file contains the master switch that enables system-wide fetchmail, the location of the fetchmail configuration file and whether the daemon should run as the root user (insecure and not recommended) or as the special user fetchmail.

Warning

Security

Running as root risks remote boot exploits. Make sure that RUNASROOT is set to false.

Do not alter these settings. 

SERVICE=true
CONFFILE=/etc/fetchmailrc
RUNASROOT=false

Modify the 'options' settings to suit your needs. For example, to run fetchmail in daemon mode polling every 30 seconds specify --daemon 30. To redirect status and error messages emitted to the system logger (syslog(3)) specify --syslog. 

OPTION="--daemon 10 --syslog"

5.3.4. Test the fetchmail daemon

Stop the fetchmail daemon. You must be the root user to do this. 

$ su
Password: *******
# /etc/init.d/fetchmail stop
Stopping mail retrieval agent: fetchmail.

You will get an error if you have an incorrect configuration. 

Stopping mail retrieval agent: system-wide fetchmail not running.)

Start the daemon. 

# /etc/init.d/fetchmail start
Starting mail retrieval agent: fetchmail.
# exit
$

You will get an error if you have an incorrect configuration. 

Starting mail retrieval agent: fetchmail (failed!)

The most likely cause of an error is a mistake in either /etc/fetchmailrc or /etc/default/fetchmail.

Once the daemon is running, sent yourself a test mail from evolution via the remote server. Connect to your provider's server, just as you did when testing Evolution's configuration, compose and send the message. 

Compose a message dialogue
   To: remote-user-name@example.net
   Subject: Fetchmail daemon test1
   Send

Give the message a couple of minutes to reach the remote server and to be returned. Keep an eye on your modem lights and you should see the regular polling of mail.example.net and the email downloading to /var/mail/local-user. Retrieve the message using evolution's Send / Receive button. 

Button bar
   Send / Receive

(Repeat as necessary.)

Hopefully, everything works correctly. evolution downloads messages just as before.

6. spamassassin

6.1. About spamassassin

Spamassassin identifies possible spam and flags it up with by adding this header to the original message: 

X-Spam-Flag: YES

6.2. procmailand spamassassin

spamassassinmust inspect and modify each message before it arrives in evolution's mailbox. One way of doing this is to intercept the mail with procmail. procmail can easily be configured to run spamassassin (see figure 6).

Figure 6: Procmail runs Spamassassin to analyse and identify spam.

This is how you start procmail. Put a hidden file called procmail in the user's root home directory. The presence of this file causes procmail to start and to follow any instructions contained in the procmail configuration file. procmail will run spamassassin if .procmailrc contains these two lines. 

:0fw 
| spamassassin

The next step is to set up a filter in evolution. The filter will move all messages with an X-Spam-Flag set to a folder called Spam instead of the normal inbox. 

Menu bar
   Tools
      Filters
Filters dialog
   Incoming 
      Filter rules
        (New)
Edit Rule dialog
   Rule name: Move to Spam folder
   If box 
      Specific header X-Spam-Flag contains YES
   Then box
      Move to folder
         Click here to select a folder
            New
               Create new folder dialog
                  Folder name: Spam
                  Folder type: Mail
                  Specify where to create the folder: Inbox
            OK
OK

6.3. Local mail

Local mail still collects in /var/mail/local-user. Previously, you would have read local mail using mail's mail command. It is best not to do this now because mail read in this way would end up in /home/local-user/mbox. You can filter on the name of local computer and divert it into a new folder called Local. (Substitute the name of your computer for local-host. You can check what this is using the command hostname .) 

Menu bar
   Tools
      Filters
Filters dialog
   Incoming 
      Filter rules
        Add
Edit Rule dialog
   Rule name: Move to local folder
   If box 
      Recipients contains @local-host
   Then box
      Move to folder
         Click here to select a folder
            New
               Create new folder dialog
                  Folder name: Local
                  Folder type: Mail
                  Specify where to create the folder: Inbox
            OK
OK

6.4. Putting it all together

Congratulations. You have now built the whole system! (See figure 7.)

Figure 7: FThe complete system. Both your external mail and your local mail arrives in your Evolution mailbox.

6.4.1. Summary of the system.

If you disabled any evolution accounts, you can now reconfigure and enable them.

7. What next?

The Woody version of spamassassin is rather old. You can keep spamassassin up to date by downloading the latest version from CPAN.

You can add vipul's razor to your system. vipul's razor allows you to report spam that gets through your current system to a database. It is a collaborative database with many contributers. vipul's razor uses the database online to weed out the spam.

A. Appendix: About this document

A.1. Copyright information

Copyright ©2004 Chris Lale . Permission is granted to copy, distribute and/or modify this document with no Invariant Sections, with no Front-Cover texts and with no Back-Cover Texts under the terms of the GNU Free Documentation License, version 1.1 or any later version, published by the Free Software Foundation. A copy of the license can be found at http://www.fsf.org/copyleft/fdl.html.

A.2. Latest version

You can get the latest version of this document from http://newbiedoc.sourceforge.net.

A.3. Bugs, errors and mistakes

If you find any errors, omissions etc, please let me know via the newbieDoc Discussion list or .

A.4. Spelling, punctuation and grammar

I have written this document in English. I have used American spellings for some technical terms eg 'program' where these have become widely accepted.

You can find guides to English spelling, punctuation and grammar at http://www.cral.ac.uk/guidelines/.

A.5. Conventions used in this document

A.5.1. Ellipsis

Three dots ...

A.5.2. Directory trees

A trailing forward slash (/) indicates that this is a directory, not a file.

A.5.3. Command line prompts

A '$' at the start of a line indicates that the rest of the line is input from a normal user. A '#' indicates that the Root user inputs the rest of the line.

A.5.4. File names, application names, package names and screen text

Filenames, application names, package names and text displayed by a console or terminal window look like this. 

my-file.txt
my-directory
/my-path/my-directory/
my-application
my-package
This is some terminal text.

Filenames, application names, package names and text displayed in an X window look like this. 

my-file.txt
my-application
my-package
This is some text in an X window.

A.5.5. Commands

Commands issued from a terminal look like this. Use of the <ENTER> key is implied but not shown. 

$ my command

This example shows a command issued in an X application. 

Menu bar:    File -> Close

A.6. Bibliography

Linux dictionary

The Linux Documentation Project's online Linux dictionary at http://www.tldp.org/LDP/Linux-Dictionary/html/index.html(online) or linux dict http://www.tldp.org/guides.html (download).

Syslog(3)

The manual page of the System Logger. Enter the command man 3 syslog at the command prompt.

Generic Mail Flow

An article in the online Linux Journal at http://www.linuxjournal.com/modules.php?op=modload&name=NS-lj-issues/issue46&file=2516s2

Debian Reference

(Osamu Aoki) Chapter 9 “Tuning a Debian system” includes brief notes about exim, fetchmail and procmail at http://qref.sourceforge.net/

Exim manual

Install the exim-doc package, then view the files in /usr/share/doc/exim.Start by looking at /usr/share/doc/exim/oview.txt with a text editor or viewer. Alternatively, install the exim-doc-html package, then view the file in /usr/share/doc/exim/manual.html/oview.html with a web browser.

A simple configuration of Exim

(Oohara Yuuma). This newbieDoc article describes how to configure Exim for local use. http://newbiedoc.sourceforge.net/networking/exim.html

Exim README.Debian

Information about the “Debianisation” of exim is held in the file /usr/share/doc/exim/README.Debian.

eximon

- X monitor for the exim mail transport agent.

Fetchmail configuration

(Oohara Yuuma) This newbieDoc article describes how to configure fetchmail. http://newbiedoc.sourceforge.net/networking/fetchmail.html