The full sendmail distribution consists of three RPM packages: sendmail, sendmail-cf, and sendmail-doc. Only the first package is truly necessary to send and receive mail on your machine. The second package includes configuration macros and other files that can help you reconfigure your site's sendmail installation if the defaults are insufficient. The third package contains documentation files that help to explain some of the details of the current version.

The sendmail binary packages are included in the Red Hat distribution. The sendmail package is on CD #1, while the sendmail-cf package is on CD #2, and the sendmail-doc package is on CD #3. From the Red Hat RPMS directory on each CD-ROM, the following command installs the packages:

# rpm -ivv sendmail*


Starting sendmail
Once installed, the sendmail service is turned on by default. To start sendmail immediately, you can either reboot the machine or just run /etc/init.d/sendmail start to start the server. The procedure for starting and stopping sendmail is no different from that of other server processes.


Other Mail Servers Available for Red Hat Linux
The open-source version of sendmail is not the only mail server available for Red Hat Linux, but it is definitely the most common. Other servers are described in the following list, with URLs that provide further information.

• Postfix — The Postfix MTA is the only mail-server software besides Sendmail that comes with Red Hat Linux. Written by Wietse Venema (of tcp_wrappers fame), this free mail server was designed with security in mind and executes most functions as an unprivileged user in a restricted chroot environment. The server encompasses more than a dozen small programs (each performing a simple, distinct task) and several single-purpose queues. Information and source code can be found at www.postfix.org.

• Exim — The Exim MTA is a free mail server (under GNU) that runs on Linux and other UNIX systems. This MTA includes enhanced protection against unsolicited junk mail and mail bombs. Find out more about Exim from the Exim Home Page (www.exim.org).

• Qmail — Also conceived with security as a high priority, this mail server (written by Daniel J. Bernstein) offers secure and reliable message transfer, mailbox quotas, virtual domains, and antispam features. More information is available from www.qmail.org/top.html.

• Sendmail (commercial version) — Based on the same source code as open-source sendmail, this product is distributed as binary executables built specifically for Red Hat Linux (among other Linux and UNIX variants). Pricing for the Sendmail Advanced Message Server is based on the number of mailboxes you are serving. The product offers simple installation, Web-based management, and support. Details can be found at www.sendmail.com.


• Smail — Smail offers many of the same features as sendmail but is somewhat easier to configure and requires less memory. The source code can be downloaded from ftp://ftp.planix.com/pub/Smail/.


Incoming messages received by sendmail are processed and stored in the /var/spool/mail directory. Each file in this directory represents a valid user name on the local machine. The file is created automatically when you add a user. People with login accounts use this directory and their user account name as their incoming mailboxes (for example, /var/spool/mail/johnq).

Outgoing messages go in /var/spool/mqueue directory while waiting to be sent. Filenames in this directory follow a consistent naming scheme. The first two characters indicate what type of data is stored in the file. Subsequent characters form a unique random identifier based on the PID of the sendmail process that is handling that message.

File Prefixes in /var/spool/mqueue
Filename Prefix	Type of Data Stored
df	The data that constitutes the body of an e-mail message.
qf	The queue control file that contains the message headers and other administrative details.
tf	A temporary copy of the qf file, created if delivery errors occur.
xf	Any error messages generated while trying to send the message.

Other programs
Several other executable programs are included in the distribution.

Other Related Sendmail Programs
Program	Description
mailq	Displays a summary of the messages awaiting processing in the mail queue (the command is equivalent to sendmail -bp).
mailstats	Displays message quantity and byte count statistics.
makemap	Translates text files (/etc/mail/virtusertable) to hashed Berkeley databases ( /etc/mail/virtusertable.db). This command runs each time the sendmail script starts at boot time.
newaliases	Translates the plain-text /etc/aliases file into the hashed Berkeley database file /etc/aliases.db (the command is equivalent to sendmail -bi).
praliases	Prints out all aliases defined in /etc/aliases.
procmail	Not included with the sendmail package, but is used as an MDA for sendmail. (It is included in Red Hat Linux in the procmail package.)
purgestat	Clears the directory where host status information is stored. The command is equal to sendmail -bH, which is disabled by default.
rmail	Handles incoming mail via UUCP.
smrsh	Implements a restricted shell for running programs from sendmail.

Logging performed by sendmail
The amount of logging performed by sendmail is configurable in the sendmail.cf file, but the default level provides good coverage of informational notices and error messages. By default, the syslog facility (/etc/syslog.conf file) stores logging information from sendmail in the /var/log/maillog file.

An informational message similar to the following is written in the /var/log/maillog file each time the daemon starts (which also causes the hashed alias database to be regenerated):

Feb 16 12:52:40 toys sendmail[1758]: alias database /etc/aliases
rebuilt by root
Feb 16 12:52:40 toys sendmail[1758]: /etc/aliases: 63 aliases, longest
10 bytes, 625 bytes total
Feb 16 12:52:40 toys sendmail[1787]: starting daemon (8.12.8):
SMTP+queueing@01:00:00

Each time a message is sent or received, a log file entry is created:

Feb 16 12:54:34 toys sendmail[1120]: OAA01120: from=root, size=161,
class=0, pri=3 0161, nrcpts=1,
msgid=<199907191254.oaa01120@toys.linuxtoys.net>, relay=root@localhost
Feb 16 12:54:35 toys sendmail[1127]: OAA01120: to=jkpat, ctladdr=root
(0/0), delay=00:00:01, xdelay=00:00:00, mailer=local, stat=Sent

The logs even show when people attempt things that perhaps they shouldn't try. The wiz and debug commands were implemented in earlier versions of sendmail and were found to be a huge security problem. You may log file entries, such as those shown in the code examples below, as people with malicious intent check to make sure that you're not running a vulnerable sendmail daemon. Also, the expn and vrfy commands (which can be disabled via a configuration option) could give out more information than you'd care to distribute.

Feb 16 13:03:27 toys sendmail[699]: NOQUEUE: "wiz" command from localhost
[127.0.0 .1] (127.0.0.1)
Feb 16 13:03:29 toys sendmail[699]: NOQUEUE: "debug" command from
localhost [127.0 .0.1] (127.0.0.1)
Feb 16 13:03:37 toys sendmail[701]: NOQUEUE: localhost [127.0.0.1]:
expn oracle
Feb 16 13:03:43 toys sendmail[702]: NOQUEUE: localhost [127.0.0.1]:
vrfy oracle


>>> Read more about What is Red Hat Linux SMTP and sendmail < <<

Source of Information : Red Hat Linux Bible: Fedora and Enterprise Edition

Several companies and organizations began gathering and packaging Linux software together into usable forms called distributions. The main goal of a Linux distribution is to make the hundreds of unrelated software packages that make up Linux work together as a cohesive whole. For the past few years, the most popular commercial distribution has been Red Hat Linux.

In September 2003, Red Hat, Inc., changed its way of doing business. That change resulted in the formation of the Red Hat–sponsored Fedora Project to take the development of Red Hat Linux technology into the future.


Red Hat forms the Fedora Project
The announcement of the Fedora Project by Red Hat, Inc. at first it prompted more questions than answers about the future direction of the company and its flagship Red Hat Linux product. In fact, it seemed that nothing named Red Hat Linux even existed anymore. Instead, what was Red Hat Linux would be reflected by Linux distributions coming from two paths:

• Fedora Project (http://fedora.redhat.com) — An open source project, beginning from a Red Hat Linux 9 base, that produces its own Linux distribution. While the project is sponsored by Red Hat, Inc., there is no official support for the Linux distribution (called Fedora Core) that the project produces.

• Red Hat Enterprise Linux (www.redhat.com/software/rhel) — An official, commercial Linux product from Red Hat, Inc. that is offered on an annual subscription basis. Red Hat backs up its Enterprise product line with technical support, training, and documentation.


The primary result of the Fedora Project (at least at first) is a set of three binary CDs and three source code CDs of a Linux distribution referred to as the Fedora Core. Before it was called Fedora Core, that distribution was being tested simply as the next in the series of Red Hat Linux distributions (presumably, Red Hat Linux 10).

The name change from Red Hat Linux to Fedora Core wasn't the only differences between the two distributions, however. Red Hat, Inc. also changed its association with the Fedora Core distribution in the following ways:

• No boxed sets — Red Hat decided to not sell Fedora Core through retail channels. The ever-shortening release cycle was making it difficult to manage this, and Red Hat believed that most of its customers were clever enough to download the software.

• No technical support offerings — There are no technical support programs available from Red Hat for Fedora Core, although at the moment you can still purchase the $60/year update service entitlement for Fedora.

• No Red Hat documentation — The set of manuals that came with the previous Red Hat Linux product is not being brought over to Fedora. Instead, a series of small task-oriented documents will be collected for the project in article format.

By not creating a whole support industry around Fedora Core, that project is free to produce software release on a much shorter schedule (possibly two or three times per year). This allows Fedora Core users to always have the latest software features and fixes included with a recent version of the operating system.

Another potential upside to Fedora Core is that the Fedora Project hopes to encourage community software developers to create compatible software. By including software download and installation tools (such as the yum utility) in Fedora Core, the Fedora Project hopes to encourage people to contribute to software repositories that Fedora Core users can rely on to download additional software packages.


Red Hat shifts to Enterprise Linux
The major shift of attention to Red Hat Enterprise Linux as the focus of Red Hat, Inc.'s commercial efforts has been on the horizon for some time. Some characteristics of Red Hat Enterprise Linux are:

• Longer release intervals — Instead of offering releases every 4 to 6 months, Enterprise software will have a 12 to 18 month update cycle. Customers can be assured of a longer support cycle without having to upgrade to a later release.

• Multiple support options — Customers will have the choice of purchasing different levels of support. All subscriptions will include the Update Module, which allows easy access to updates for Red Hat Enterprise Linux systems. The Management Module lets customers develop custom channels and automate management of multiple systems. The Monitoring Module allows customers to monitor and maintain an entire infrastructure of systems.

• Documentation and training — Manuals and training courses will center on the Red Hat Enterprise Linux distribution.

Red Hat Enterprise Linux install types focus on three different types of computer systems, referred to as WS (for workstations), AS (for high-end systems), and ES (for small/mid-range servers). Each system in the Red Hat Enterprise Linux family is meant to be compatible with the others. There are Basic, Standard and Premium editions of these Enterprise systems. While Basic offers only software downloads, standard and premium editions offer hard copy documentation and additional technical support.


Choosing between Fedora and Enterprise
There is so much overlap between Fedora Core and Red Hat Enterprise Linux, Fedora Core provides a way to test out much of the software that is in Enterprise editions.

Although Fedora Core may not be right for everyone, Fedora Core is still great for students, home users, most small businesses, and anyone just wanting to try out Red Hat Linux technology. Larger businesses should seriously consider the implications to support, training, and future upgrade paths before choosing whether to go the Fedora route or sign on with Red Hat Enterprise Linux.

Source of Information : Red Hat Linux Fedora For Dummies

Linux is freely available software. The source code for Linux, which is the heart and soul of the operating system, is also publicly available. The Free Software Foundation (FSF) contributes much of the utilitarian software that makes using Linux much easier — FSF is the brainchild of the great Richard Stallman.

Red Hat Linux combines all those pieces plus some additional applications and then goes another step and adds a few of its own to create an integrated product. Red Hat, Inc., combines the basic Linux operating system with software (some made by other companies and some made by Red Hat) to produce a package with a value that’s greater than the sum of its parts. That combination is known as a distribution, or flavor, of Linux.

Red Hat Linux was initially used almost solely to provide network services. However, Red Hat started working hard to make Linux suitable for your everyday use. The result is that Red Hat Linux is now used in both server and desktop environments. It’s used by individuals, businesses, and governments to cut costs, improve performance, and just plain get work done.

You can use Red Hat Linux as a desktop workstation, a network server, an Internet gateway, a firewall, the basis of an embedded system (such as a smart VCR or a robot), or even as a multiprocessor supercomputer. And, thanks to the many, many people who continually make refinements and innovations, Red Hat Linux continues to become more flexible and capable with each release.

The Linux operating system has been ported (or converted) from the 32-bit Intel architecture to a number of other architectures, including Alpha, MIPS, PowerPC, and SPARC. This conversion gives users a choice of hardware manufacturers and keeps the Linux kernel flexible for new processors. Linux handles symmetric multiprocessing (it can take on more than one CPU or mathematical and logical programming unit per system box). In addition, projects are in the works to provide sophisticated processing capabilities, such as

Real-time programming: Controlling machinery or test equipment.

High availability: Running a server that needs to work all the time.

Parallel processing: Amplifying the problem-solving power of a computer by using multiple processors to work in parallel. Parallel processing systems come in various flavors, such as Symmetric Multi Processing (SMP), extreme Linux systems, and Beowulf clusters. Research organizations and even individuals can create machines with supercomputer capabilities at a fraction of the price of supercomputers. In certain cases, extreme Linux systems have been made from obsolete PCs, costing the organizations that make them nothing in material costs.


This list shows some cool Red Hat Linux features you can use:

• Desktop productivity tools: Red Hat has successfully worked overtime over the past few years to make Linux work on your desktop. Red Hat bundles software, such as the OpenOffice suite of productivity tools, so that you can get your everyday work done. The OpenOffice suite includes a full-function word processor plus spreadsheet, presentation, graphical drawing, and Web page creation tools. Its word processor can read and write all Windows Office formats plus many others, such as WordPerfect. When you install Red Hat Linux, OpenOffice is installed and icons are placed on the menu bar to make accessing it easy.

• Multimedia stuff: Red Hat Linux packs numerous multimedia tools for you to use. You can play, record, and rip audio tracks from CDs and DVDs. You can listen to streamed media sources, such as radio stations, over the Internet. Linux also lets you transfer photos and other items from your own cameras and MP3 players, for example.

• Network services: Red Hat Linux works as a network-based server too. Linux found its initial popularity performing jobs like Web serving and file and printer sharing and hasn’t missed a beat.


Boosting your personal workstation
We cannot emphasize enough how well Red Hat Linux works as a personal workstation. With Red Hat Linux, you can easily create your own, inexpensive, flexible, and powerful personal workstation. Linux provides the platform for most of the applications you need to get your work done. Many applications come bundled with Red Hat Linux, from desktop productivity suites, to web browsers and multimedia systems, for example.

The following list describes just a few major categories of free software available for Linux, along with some examples of popular programs:

• Office suites: OpenOffice provides a complete desktop productivity suite that includes an advanced word processor, a spreadsheet, and a presentation editor, for example. The OpenOffice word processor can read and write Microsoft Word files, HTML editors, spreadsheet editors, and graphics editors. OpenOffice provides its own file format but also reads and writes Microsoft Office 97, Office 2000, and Office XP files. It also can use other formats, such as Rich Text Format. Check out the site, at www.openoffice.org.

• Multimedia players: Red Hat packages and installs the open source XMMS player. You can use XMMS to play downloaded Ogg/Vorbis files or continuous Ogg/Vorbis streams. You can download the excellent open source MPlayer audio and video player. MPlayer lets you watch DVDs and listen to MediaPlayer streams. You can, alternatively, download a free version of the proprietary RealPlayer, from RealNetworks, to listen to RealAudio streams. The Internet is going nuts with multimedia, and these multimedia players let you get in on the action.

• Running Microsoft Windows applications and environments: You can use Linux to run Windows programs. The WINE (Wine Is Not an Emulator) system facilitates running Windows programs directly under Linux. The commercial VMware workstation product creates a virtual computer within your Linux PC. The virtual machine looks, acts, smells, and performs just like a real computer, but is really just a program running under the Linux operating system. You can install Linux or Windows or both on the virtual machine. Both WINE and VMware create a bridge between Linux and Windows to give you the best of both worlds.

• Web browsers and e-mail clients: The open source browser, Mozilla, is included with Red Hat Linux 10. The nongraphical, text-based lynx and links browsers are included too and come in handy if you’re using an older, slower modem because they don’t require as much speed as Mozilla does. You can use Mozilla or the new Ximian Evolution personal organizer, calendar, and e-mail client.


Using Linux network tools and services
Linux computers can provide many powerful and flexible network services.

• Apache web server: Of all the web servers on the Internet, the majority are run by the open source Apache web server.

• OpenSSH: The open source version of Secure Shell enables you to communicate securely across the Internet. Secure Shell is much safer than Telnet because Secure Shell encrypts your communication when you log in (even when you log in to other computers), making much slimmer the chance that others can discover your passwords and other sensitive information. OpenSSH also provides other authentication and security features and enables you to securely copy files from machine to machine. With OpenSSH, you can prevent people from listening to your communication.

• Internet accessing utilities: Red Hat Linux provides several configuration utilities that help you connect to the Internet. The utilities help you to configure DSL, cable modems, and plain old telephone modems to connect to the Internet. They also help you to connect to Local Area Networks (LAN) using Ethernet adapters.

• Firewalls: A firewall is a system that controls access to your private network from any outside network (in this case, the Internet) and to control access from your private network to the outside world. To keep the bad guys out, Red Hat Linux provides protection by giving you the tools to build your own firewall. Red Hat Linux is flexible in this regard, and many software packages are available, including the popular and simple-to-use netfilter/iptables filtering software.

Source of Information : Red Hat Linux Fedora For Dummies

With the recent split between community (Fedora) and commercial (Red Hat Enterprise Linux) versions of Red Hat Linux, Red Hat has created a model that can suit the fast-paced changes in the open source world, while still meeting the demands for a well-supported commercial Linux distribution.

Technical people have chosen Red Hat Linux because of its reputation for solid performance. With the new Fedora Project, Red Hat hopes to create an environment where open source developers can bring high-quality software packages to Red Hat Linux that would be beyond the resources of Red Hat, Inc. to test and maintain on its own.

Over 1,400 individual software packages (compared to just over 600 in Red Hat Linux 6.2) are included in the latest release of Red Hat Linux, referred to as Fedora Core. These packages contain features that would cost you hundreds or thousands of dollars to duplicate if you bought them as separate commercial products. These features let you:

• Connect your computers to a LAN or the Internet.

• Create documents and publish your work on paper or on the Web.

• Work with multimedia content to manipulate images, play music files, view video, and even burn your own CDs.

• Play games individually or over a network.

• Communicate over the Internet using a variety of Web tools for browsing, chatting, transferring files, participating in newsgroups, and sending and receiving e-mail.

• Protect your computing resources by having Red Hat Linux act as a firewall and/or a router to protect against intruders coming in through public networks.

• Configure a computer to act as a network server, such as a print server, Web server, file server, mail server, news server, and a database server.

This is just a partial list of what you can do with Red Hat Linux. There are many more features built into Red Hat Linux as well.

Support for new video cards, printers, storage devices, and applications are being added every day. Linux programmers around the world are no longer the only ones creating hardware drivers. Every day more hardware vendors are creating their own drivers, so they can sell products to the growing Linux market. New applications are being created to cover everything from personal productivity tools to programs that access massive corporate databases.

Remember that old Pentium computer in your closet? Don't throw it away! Just because a new release of Red Hat Linux is out doesn't mean that you need all new hardware for it to run. Support for many old computer components get carried from one release to the next. There are old PCs running Red Hat Linux today as routers (to route data between your LAN and the Internet), firewalls (to protect your network from outside intrusion), and file servers (to store shared files on your LAN) — with maybe an Ethernet card or an extra hard disk added.

Source of Information : Red Hat Linux Bible - Fedora And Enterprise Edition