Unix has always have been e-mail ready, and Linux is no exception

E-mail has always been integral to Unix. Even the earliest commercial Unix systems had some sort of e-mail facilities built-in. This is a legacy of the deployment of the OS in US colleges including University Of California At Berkeley (UCAB) where a large amount of communications research for building the intranet was done.

Linux, being a Unix variant, also boasts of a full range of products for e-mail handling and delivery. While it can be used as a mail client (it contains stuff like "pine", known to anybody who has ever used VSNL’s shell account, and "elm", another popular e-mail front end), where it really comes into its own is as a mail server.

For intranet mail, you need to have a mail delivery agent running on the mail server, which can be the same machine on which you have your Webserver and your DNS server and other intranet software running. Virtually every distribution of Linux comes with a mail server and usually it is installed along with the OS itself. The two most popular mail servers for Linux are sendmail and smail and the latest versions of both are available for download from many places on the Internet. One popular site is sunsite.unc.edu.

We installed sendmail for Linux from our Slackware distribution CD-ROMs. Smail too is a good option, especially, if the network is small and needs something that is easy to manage. Sendmail is more difficult to use but is more flexible.The sendmail program can also be run as a daemon right from startup and that seems to be the preferable way. To startup the program, the superuser (root) just has to type "sendmail –bd –q15m" at the command prompt. The "-bd" flag is to enable it to run as a daemon process and the "-q" flag asks it to process the mailqueue every 15 minutes. Of course, there are many other options but these two are usually enough. Sendmail automatically sorts intranet and outbound mail and ensures that all outbound mail goes into a mailqueue.

To send e-mail to other systems (Internet e-mail) you have to connect to the Internet through a dial-up line. One way of doing so is the "dip" utility. This is a very versatile program designed to handle TCP/IP sessions. It allows others to login into your machine and also allows your server to dial out and use PPP or SLIP to login to other servers. The syntax of the command for dialing out is "dip <filename>". Here <filename> has to be a special script containing a list of dip commands. One such "dipscript", customized for Indian conditions is available at www.pcquest.com (Archives, May 96, Comversations). Look at the article Linux and the Internet.Mail within the network is easily handled by the sendmail daemon. Just create users for every person in the company who needs an account (use the "adduser" command) and relax after that. The system handles all mail to and from the accounts, without the need for administrator intervention at all.

Obviously, it is unreasonable to expect all the users to learn Unix just to send and receive mail. What is needed is a Post Office Protocol system to enable the users to upload and download mail from the server while still reading, writing, and editing it from their desktops running Win 95 or Mac or something like that. Fortunately, setting up POP account for the users is also very easy and involves little or no manipulation from the server side. Usually, the system initializes the pop2d and pop3d daemons during startup along with the rest of the inet daemons (telnet, ftp etc). However, just to make sure, open the file "/etc/inetd.conf" and search for the following lines:
pop2 stream tcp nowait root /usr/sbin/tcpd in.pop2d
pop3 stream tcp nowait root /usr/sbin/tcpd in.pop3d

If these do not exist then put them in, if these exist but have a "#" at the beginning, then the pop server have been disabled, so just remove the "#" and read on. If you are lucky, the lines exist and are unhashed already, then relax and quietly exit the file cause your server is already setup and ready to act as pop server too. You probably don’t need to read the rest of this section and can directly move on to setting up the client side. If you do not have these lines, don’t worry too much, just put them in, remembering to put exactly one tab between every two fields.

Type "ps" after logging in as root and identify the PID of the inetd daemon. Then give the command "kill –HUP <pid-of-inetd>". This forces the inetd daemon to read the inetd.conf files again and thus initialize the pop daemons too. Once this is over we are ready to move to the configuration of the client side programs.

Setting up the mail client

In order for individual users to be able to send and receive mail, they need to use an e-mail client on their machines. This can be anything from browsers like Navigator and Explorer which integrate mail clients into themselves to dedicated e-mail clients like Eudora. Configuring the mail client is quite an easy job. Simply put in the IP address of your mail server and your e-mail ID. Once this is done, you are ready to log in with your password and send and receive mail.