16.2.1. The Postfix MTA

Several MTAs are available for Linux. Historically, the most common MTA on Unix has been Sendmail, which has been around for a long time. It is generally considered somewhat more difficult to use than the alternatives, but it is thoroughly documented in the book sendmail by Bryan Costales with Eric Allman (O'Reilly).

Postfix is a newer MTA, developed by security guru Wietse Venema as a replacement for Sendmail. It's designed to be compatible with Sendmail but to provide a higher level of security and be easier to configure.

Postfix is a highly flexible and secure piece of software that contains multiple layers of protection against would-be attackers. Postfix was also written with performance in mind, and employs techniques to limit slower activities such as creating new processes and accessing the filesystem. It is one of the easier email packages to configure and administer because it uses straightforward configuration files and simple lookup tables for address rewriting. It is remarkable in that it is simple to use as a basic MTA, yet still able to handle much more complicated environments.

16.2.2. Getting the Mail to Your Computer with Fetchmail

If your provider stores your mail for you until you fetch it, and you do not want to use your mailer to download the mail, you need a program that retrieves the mail from your provider's computer. There are a lot of programs for doing this; we will discuss fetchmail here briefly because it is both robust and flexible and can handle both POP3 and IMAP.

You can get fetchmail from your friendly Linux archive; chances are that your distribution carries it, too. In case you download a source distribution of fetchmail, unpack, build, and install it according to the installation instructions. At the time of this writing, the current version is 5.9.13.

You can control fetchmail's behavior via both command-line options and a configuration file. It is a good idea to first try to fetch your mail by passing the necessary information on the command line, and when this works, to write the configuration file.

As an example, let's assume that my provider is running the POP3 protocol, that my username there is joeuser, and that my password is secret. The hostname of the machine where the POP3 server is running is mail.isp.com. I can then retrieve my mail with the following command:

fetchmail --protocol POP3 --username joeuser mail.isp.com

fetchmail then asks me for my password and, after I specify it correctly, retrieves the mail waiting for me and passes it on to my MTA for further delivery. This assumes that a SMTP server is running on port 25 of my machine, but this should be the case if I have set up my MTA correctly.

While you are experimenting with fetchmail, it might be a good idea to also specify the option — keep. This prevents fetchmail from deleting the messages from your POP3 account. Normally, all messages are deleted from your provider's hard disk once they are safely stored on your own machine. This is a good thing because most providers limit the amount of mail you can store on their machines before retrieving them, and if you don't delete the messages after fetching them, you might reach this limit quite quickly. On the other hand, while testing, it is a good idea to be on the safe side and use — keep so as not to lose any mail.

With the aforementioned options to fetchmail, you should be able to get your mail in most cases. For example, if your provider uses the newer IMAP protocol, simply specify IMAP in the command line instead of POP3. If your provider has some unusual setup, you might need one of the other options that the fetchmail(1) manual page tells you about.

Once you are satisfied with the download process, you can write a fetchmail configuration file in order not to have to enter all the options each time you use the command. This configuration file is called .fetchmailrc and should reside in your home directory. Once you are done editing it, make sure it has the permission value 0600 so that nobody except yourself can read it because this file might contain your password:

chmod 0600 ~/.fetchmailrc

The full syntax of the configuration file is detailed in the fetchmail manpage, but in general you need only very simple lines that start with poll. To specify the same data as on the command line in the previous example, but this time include the password, put the following line into your configuration file:

poll mail.isp.com protocol pop3 username joeuser password secret

Now you can run fetchmail without any parameters. Since fetchmail already knows about your password from the configuration file, it will not prompt you for it this time. If you want to play it safe while testing, add the word keep to the poll line.

Using fetchmail with a configuration file has one additional advantage: you can fetch mail from as many mailboxes as you want. Just add more poll lines to your .fetchmailrc, and fetchmail happily retrieves your mail from one server after the other.

When and how you run fetchmail depends on your connection to the Internet. If you have a permanent connection or a cheap, flat rate, you might want to have fetchmail invoked by cron at a suitable interval (like once an hour). However, if your Internet connection is nonpermanent (dial-up) and costly, you might want to choose to run fetchmail by hand whenever you actually want to fetch and read your mail so as to minimize your Internet connection time. Finally, if you are using PPP for dialing in to your Internet service provider, you might want to invoke fetchmail from the ip-up script, which is invoked as soon as an Internet connection is made. With this setup, when you browse a web page and your computer dials up your provider, your mail is fetched automatically.

16.2.3. Other Email Administrative Issues

16.2.4. Using KMail

Figure 16-4. KMail mailer

Figure 16-5. KMail identity configuration

Next, go to the Network configuration group. Here, you need to create at least one account for outgoing mail and one for incoming mail.

Figure 16-6. KMail identity for outgoing mail

This should be enough to let you send outgoing email, but we recommend that you take a few additional steps to make this as secure as possible. KMail makes this easy for you by autodetecting the security settings of the SMTP server you are using. Go to the Security tab and click the button labelled "Check what the server supports." KMail will check the connection to the server and use the settings with the highest supported security. Alas, many providers run their mail servers without any security at all.

Now let's continue by configuring the receiving end. Close all subdialogs until you are back at the Network configuration group, and select the Receiving tab. Here you can set up a number of accounts to be queried. This can be useful if you have more than one provider that stores email for you. Click the Add... button and select the type of mail server. If you run your own MTA locally, you need to select Local Mailbox. Usually, you can then accept the defaults on the next page (but change the name to something more appropriate than "Default").

If you retrieve your messages directly from your provider's server, you need to select either POP3 or IMAP, depending on what your provider supports. In the dialog that appears again enter a name of your own choice, then specify your login name, your password, the name of the host that stores your email, and the port (usually 110 for POP3 and 143 for IMAP). All this information should be given to you by your provider or system administrator. You can leave all other options as they are for now, and experiment later with them.

Close all dialogs with the OK button. You should now be ready to retrieve your email. To do so, select File Check Mail from the menu. This will retrieve all messages from all incoming mailboxes that you have specified. If it does not work or you get any error messages, check all the values you entered on the various configuration pages again and compare them to the information given to you by your provider or system administrator. The most typical error is a typo in the hostname, username, or password.

In order to send a message, press Ctrl-N or select Message New Message. A composer window opens where you can type in the recipient's address, the subject, and the actual message body. If you have configured more than one identity, you can also select the one to be used for this message. When you are done composing your message, press Ctrl-N. Depending on how you have configured your outgoing mail transport, the message will either be put into the output folder and wait there for further handling (this is the default) or be transmitted directly. If you want to override your setting for a particular email, just select Message Queue or Message Send Now from the menu bar of the composer window.

Messages put into the output folder are by default not sent automatically (you can, however, configure KMail to always send messages in the outbox when it checks for incoming messages). To send all messages in your outbox, select File Send Queued from the menu bar of the main KMail menu.

If you have problems sending your messages, again please check the settings you have made for typos. Also, in order to prevent the relaying of unsolicited commercial email (so-called spam) via their servers, some providers require that you check your mailbox on the server (providing your username and password as you go) in order to identify yourself, before you can send any email via that server. After you have checked your incoming email, you have a certain period of time (often 15 minutes) to send your outgoing email.

You should now know enough about how to use KMail in order to continue exploring the mailer on your own. One of the first things you may want to do (especially if you have a large number of messages to handle everyday!) is to create folders by selecting Folder Create and then set up filters by selecting Settings Configure Filters. This lets you redirect messages with certain characteristics (e.g., certain senders or subjects) to predefined folders. For example, you may want to gate all messages from a mailing list to a folder dedicated to that purpose.

16.2.5. Using Mozilla Mail & News