Extension developers have also added several interesting add-ons for the email client including the previously reviewed Sender Verification extension.

Quick Filter is another extension for Thunderbird 3 that adds email filtering capabilities to the web browser. The extension adds a small toolbar on top of the email column in the software program that can be used to filter the emails of the active folder in Thunderbird.

Five permanent filter options are displayed in the toolbar plus a text form to filter the emails by name.

The permanent filter options are there to display only unread or starred emails, emails send by contacts, emails by tag or emails with attachments. These email filters can be combined with the text filter to quickly find specific emails in the active folder.

The extension searches in the sender, recipients and subject header by default with the option to add the body text to search the email body as well. These filters can be configured as needed, it is for instance possible to only search in email bodies or by sender.

Another interesting option provided by the email filtering extension is the ability to make the filter settings permanent so that they are applied to other folders the user switches to. This can be enabled or disabled in the toolbar as well.

Quick Filter is a very handy extension for the Thunderbird email client that is most useful to filter emails in large mail folders.

The extension has now been integrated into Thunderbird 3 and therefor removed from the add-on repository.

Fortunately there is a tool for that. The tool? Spamassassin. Spamassassin is a very versatile SPAM tool that is part of the Apache Foundation. Spamassassin uses numerous means to detect SPAM including: DNS and Checksum based SPAM detection as well as Bayesian filtering, external programs, black lists, and online databases. These tools together make for a fairly powerful detection system.

In this article you are going to see how to install and configure Spamassassin to work in conjunction with Postfix to further enhance your email server.

Installing Spamassassin

Obviously the first thing you need to do is install Spamassassin. You will find Spamassassin in the Ubuntu repositories. And since this entire series has been laid on top of a Ubuntu Server installation, that is quite convenient. So, to install Spamassassin, open up your terminal window and issue the following command:

sudo apt-get install spamassassin

There may or may not be some dependencies to install in order for the Spamassassin  installation to complete. Go ahead and OK those. Once this installation is complete you are ready to start configuring.

Configuration

Before we actually get to the configuration it is important to understand the SPAM scoring system. With Spamassassin, messages are tagged as SPAM only when they have enough SPAM-matching characteristics (according to a scoring level). The scoring level is 0-5, however it’s not as simple as saying a 0 means it is 0% SPAM. The system is set up so that every characteristic can add to the overall score. For example a message tested to find a base64 attachment does not have a file name filtered with both bayes+net will add 0.224 to the over all score of the message. When all of the characteristic scores are added up, if they exceed the default score you have set in the configuration file, that message is considered SPAM.

Now that you have a basic understand of how the scoring system works. Let’s start configuring Spamassassin.

The main configuration file is /etc/spamassassin/local.cf. The first option you want to configure is the default score. Look for the line:

# required_score 5.0

The first thing you want to do is uncomment that line (by removing the “#” character) and then changing the score. A score of 5 is pretty high and sure to be SPAM. Understand the more you lower that score the likely you are of missing message messages that are tagged false-positives. A score of 3.5 is a fairly reliable score that will catch a lot of SPAM but not a lot of false positives.

Above this line are a couple of other options that are important. The first is the option to set the option:

report_safe

To 0. This option can be set to either 0 or 1. A zero means that if a message is found to be SPAM the message will not be deleted, but instead the subject line will be rewritten to include a message marking it as SPAM.  This is handy to prevent users from losing important messages to false positives. This also allows you to set a lower score threshold.

To do this first look for the line:

# report_safe 1

Uncomment this line by removing the “#” character and then change the “1″ to “0″ (no quotes).

The next step is to uncomment the line:

# rewrite_header Subject *****SPAM*****

Now you can alter the “*****SPAM*****” section of this line to reflect what you’d prefer it to say. Just make sure it is clear to your users that a message with this rewritten subject line is most likely SPAM.

Now restart the Spamassassin daemon with the command:

sudo /etc/init.d/spamassassin restart

Configure Postfix

The last step is to set up Postfix to use Spamassassin. To do this open up the file /etc/postfix/master.cf and look for the line:

smtp     inet    n   –   –   –   –   smtpd

You need to alter this line to look like:

smtp      inet   n   -   -   -   -   smtpd -o content_filter=spamassassin

Finally, at the end of this file add the following:

spamassassin
unix - n n - - pipe
flags=R
user=spamd
argv=/usr/bin/spamc
-e /usr/sbin/sendmail
-oi -f ${sender} ${recipient}

Now all you need to do is restart Postfix with the command:

sudo /etc/init.d/postfix restart

Your mail server should now be scoring incoming message as SPAM or HAM.

Final thoughts

The mail server is a tricky beast. You have to ensure that users are getting their mail, but you have to make sure they aren’t receive SPAM or viruses. After completing this series of articles, you should have a pretty solid server running that will send out mail that is safe for users eyes.

One of the aspects of Claws Mail that I like more than that of either Thunderbird or Evolution, is the filter tool. I am sure you know that email filters are one of the best means to manage the enormous amount of email coming down the pipe. You can keep SPAM in the trash, filter specific email to specific folders, and take just about any kind of action you need/want.

For many, the Claws Mail filters might not be as simple to use as the standard fare. But that doesn’t mean they shouldn’t be used.  With this tool, it is just a matter of getting used to a different interface. And that is what this article will help you with.

The tools

There are two ways to create a filter with Claws mail: The easy, less configurable method, or the harder, more configurable method. I will only briefly mention the easy method as that is, well, easy. The second, harder, method is what we will primarily focus on.

The easy method

If you have an email selected, click on the Tools menu and then select “Create Filter Rule”. When this new sub-menu pops up you will see four entries:

• Automatically
• By From
• By To
• By Subject

That will define the condition of the filter automatically for you. You will still have to configure the rest of the filter, but this step automates a portion of the creation.

Now let’s take a look at the full creation of a filter by doing things the hard way. I shouldn’t scare you off by saying “hard way”…it’s not really that difficult.

Filter from scratch

Figure 1

When you go to the Configuration menu you will see the Filtering entry. Click that to open up the Filters window (see Figure 1).

As you can see, for the most part, creating a filter is simple. The only aspect that might not be as user-friendly as you are used to is the Conditions and Actions. For these what you have to do is is click the associated Define buttons.  When you do this you will configure the specifics of either the conditions or the action of the filter. Let’s take a look at configuring the conditions of a filter. Click the Define button associated with the Conditions. When you do this a new window will open up.

Figure 2

Figure 2 shows a condition already created. What you can not see, from the image, are the included options in the drop down lists. With different types of filters you will have different drop down lists available. The different types of criteria you can select include: Header, Age, Phrase, Flag, Color lables, etc. Say you select the Header from Match Criteria. When you do you can then select:

Name: From this drop down you can then select such familiar items as To, From, Reply To, etc.

Header: This is where you decide if your header Contains or Doesn’t Contain. Basically this is a positive or negative match.

Once you have your condition rule set you then click the Add button. If you want you can then create more rules for this one condition. Each condition can have multiple rules and you can move the rules up or down in the chain of command. You can also configure if the rule must meet all or at least one of the rules.

Figure 3

When you are finished with your Condution click OK and it is set. You are now ready to define your Action. Click the Define button associated with Action which will open up a new window (see Figure 3).

This is the easier portion of the setup. What you do is select what action you want to take from the Action dropdown and then select the associated sub-action. The associated action will depend upon which Action you choose. For instance, if you select to Move the mail you will then have to select the Destination folder. If you want to flag the message you will have to select how you want it flagged.

Once you have completed this section click OK. Now, before you finalize the new Filter you have to click the Add button in the main window. If you do not do this your newly created filter is not saved. You will get a warning if you try and then click the Continue Editing and then click the Add button.

Your filter is complete. You can test this by click the Tools menu and selecting Filter All Messages in Folder. If your folder is set up correctly you will see the changes made instantly.

Final thoughts

Claws Mail filtering is a very powerful tool that will allow you to create very helpful filters to keep your Claws Mail organized and free from unwanted email.