# LPI Linux Certification/LPIC2 Exam 202/Mail & News

* LPIC2 Exam 202
* Detailed_Objectives
* Networking
* Basic networking configuration
* Advanced Network Configuration and Troubleshooting
* Mail & News
* DNS
* Web Services
* Network Client Management
* System Security
* Network Troubleshooting
* Exercises results

## Section Overview

* Configuring mailing lists
* Using sendmail
* Using Postfix
* Managing mail traffic
* Serving news
* Configuring mailing lists

## Configuring mailing lists

Majordomo is a mailing list management program. Its goal is to handle all incoming mails to a particular email address, and re-distribute them to a list of email addresses. Majordomo also handles adding and deleting an email address from its lists.
Since Majordomo is responsible for managing E-mail lists, Majordomo relies heavily on a MTA such as Sendmail, Smail, Qmail or Postfix.
aliases file (usually /etc/aliases) is used for making aliases for E-mail addresses. For example, once Majordomo is installed, usually an entry in the aliases file reads:
This entry means that all mail addressed to majordomo-owner@host.com will actually be sent to jarchie@host.com. Notice it is unnecessary to append the @host.com to jarchie because both users are on the same host. If it were desired to redirect the message to a different user on a different host, one would have to add the @host.com portion.
Another type of entry in the aliases file allows E-mail to be redirected to multiple addresses listed in a file:
testlist: :include:/usr/local/majordomo-1.94.5/lists/testlist
This entry states that any message sent to testlist@host.com will be redirected to all the addresses listed in the file /usr/local/majordomo-1.94.5/lists/testlist. The testlist file might look something like this:
Majordomo is able to add or remove addresses from a list by taking advantage of this feature. When a subscribe request is processed, the user's E-mail address is appended to the testlist file; when an unsubscribe request is processed, the user's E-mail address is removed from the testlist file. One can also add or remove addresses manually simply by editing the file with a text editor such as vi.
Since Majordomo needs to be able to process commands sent to it via E-mail, Sendmail must be able to execute the Majordomo program and pass the message to it. This is done by adding another type of entry to the aliases file:
The program /usr/local/majordomo-1.94.5/wrapper is a wrapper (SUID and SGID majordomo or daemon depending on the configuration) that runs the Majordomo program. The quotation marks around the second part of the alias entry are used to tell Sendmail that this part of the entry is all one statement; the quotation marks would be unnecessary if there were not a space between wrapper and majordomo. The | is known as a "pipe"; it is used to tell Sendmail to send the E-mail to the wrapper via the standard input. (Since all the wrapper does here is to call majordomo, the E-mail is actually being sent to Majordomo.) The wrapper accepts one parameter--the parameter of the program it is supposed to execute. (Any parameters after the first will be passed to the program the wrapper is executing.) For security reasons, the wrapper only executes programs located in the Majordomo directory, /usr/local/majordomo-1.94.5/. This restriction prevents a programmer from using the wrapper to run programs that should not have Majordomo privileges. (i.e, wrapper /bin/vi would allow any user to edit any Majordomo configuration file.) When a message is sent to majordomo@host.com, Sendmail starts up the wrapper which, in turn, starts up majordomo, and Sendmail sends the message to the majordomo script via the standard input. Majordomo then extracts the commands out of the message and responds appropriately.
Majordomo is, of course, the piece of code that this document revolves around; it consists of a collection of Perl scripts with the sole purpose of managing mailing lists.
Majordomo must run under a specific UID and GID so when any of the scripts are run, they will run under Majordomo's UID. Thus, it is necessary to decide what UID and GID Majordomo should run under. Also, Majordomo must be a Sendmail trusted user
Check the /etc/passwd and /etc/group files to find a UID and GID that are not taken. For this example, a UID of 16 and a GID of 16 was chosen. You have to decide on the location where the Majordomo scripts will reside. If you are using a shadowed password file, add entries similar to
to your /etc/passwd and add an appropriate entry to /etc/shadow.
Use the other entries in these files as a guide for exactly what should be added. These are only the values for my system. If you are not using shadowed passwords, only an entry in the /etc/passwd file is necessary.
To create a Majordomo group, add a line similar to
to your /etc/group file. Appending your username to the end of the line will give you access to the Majordomo files that are group writeable.
The Makefile contains all the information needed to install Majordomo; it is usually necessary to edit lines in the Makefile that refer to system specific settings so Majordomo will be able to install cleanly on your system. Most of the default settings are correct; however, the following settings, almost invariably, need to be changed on a per system basis.
should be changed to something more appropriate for your system. For example, in my setup, the values were changed to
Also the majordomo.cf file must be created. An easy way to create this file is to copy the provided sample.cf file to majordomo.cf and edit it.
Again, most of the settings are correct by default, but the following lines might need to be changed for your system from :
to something more appropriate such as
$whoami and $whoami_owner do not need to be changed for Majordomo to work; however, I changed them because I like to avoid typing capital letters. $digest_work_dir is a temporary directory where digest files should be placed; this directory should be assigned to wherever you want digests to be stored. If you do not plan to use digested lists, do not worry about this option. $whereami, $homedir, and $sendmail_command should be changed to appropriate values for your system. Unlike the Makefile, these options can always be changed after Majordomo is installed by editing majordomo.cf in the directory where Majordomo was installed. (The configuration file is simply copied during setup.)
The next step is to compile the Majordomo wrapper. The wrapper is the only Majordomo component that needs to be compiled because everything else is a collection of perl scripts and, therefore, is not compiled.
To install the Majordomo files, execute the commands
The first command can be done as the Majordomo user (assuming majordomo can create or has access to $home_dir), but the second command needs to be done as root so the installation script can SUID root the Majordomo wrapper. (Since, majordomo was created without a login shell or password, if you want to execute the first command as majordomo, you will need to su majordomo as root in order to become majordomo.)
Sendmail aliases must be created for Majordomo so commands sent to Majordomo can be processed by majordomo, and an alias for the Majordomo owner must be created so people can E-mail you through the standard owner-majordomo address. Add the following entries to your aliases file :
Then test your configuration, as a regular user (not as majordomo or as root), run :
This program can detect most problems in the Majordomo installation.
To create a list, create a file with the name of the list in the Majordomo lists directory. For example, to create a list called test, create a test file as Majordomo :
and add the related aliases :
Now test the operation of the list by issuing a lists command to Majordomo :
It should only take a second for majordomo to reply with a message containing all the lists which are currently set up. Next, try issuing a help command.
Majordomo should reply with a list of all commands that Majordomo accepts. It might be a good idea to save the message for future reference.
To see if the aliases are working properly, try subscribing and unsubscribing yourself to the list :
You will receive an E-mail message containing instructions on how to confirm your subscription as well as a letter confirming that your command was successful. After sending back your confirmation, Majordomo should send back two letters--one letter stating that your subscribe request was successful and another letter welcoming you to the test list. The owner of the list will also be sent a message stating that you have subscribed to the list.
To unsubscribe from a list, send a unsubscribe command
You should be sent back a letter stating that your command was successful.
For some lists, it may be desirable to have Majordomo process messages before they reach the list. For example, Majordomo has the resend script to automatically filter messages based on content (such as taboo words), to prevent people from sending Majordomo commands to the list, and other features. To use these options, it is necessary to use a better set of aliases such as :
The last entry allows someone simply to send a message to test-request@kes.emeraldis.com with the text subscribe rather than sending a letter to majordomo@kes.emeraldis.com with the text subscribe test. Also, note that if sendmail is using smrsh, the above aliases should reference the copy of the wrapper in the safe path--usually /etc/smrsh/wrapper.
It is common for Majordomo's permissions to be set incorrectly causing Majordomo to work improperly. Fortunately, Sendmail and Majordomo typically, give decent error messages indicating a problem. For example, the lists directory must be executable by the user sendmail setuids to, typically mail or daemon. If sendmail cannot execute lists, the permissions must be loosened.
Another common problem is caused by the lists directory being group writeable. To solve this problem, one can ether clear the group writeable bit, or use the sendmail option IncludeFileInGroupWritableDirPath
Majordomo is intended to run on a isolated system; there are a couple of well-known security holes in the scripts that allow any local user capable of executing wrapper to execute code as the majordomo user. If Majordomo must be run on a system providing users with shell access, then it is advisable to tighten up permissions on the wrapper. This can be done by clearing the world executable bit and chgrping the wrapper to the user that needs to run the Majordomo scripts. For example, if Sendmail and MajorCool are both being used to execute the wrapper use the commands
to secure the system. This will allow sendmail (while running under mail) to execute /etc/smrsh/wrapper while allowing the webserver's MajorCool (running under nobody) to execute /usr/local/majordomo-1.94.5/wrapper. This solution, however, will allow anyone with the UID or GID of mail or nobody to also obtain access to the majordomo account. To protect the nobody account, it is important not to allow normal users to make use of server side includes or cgi scripts unless those services do not run under nobody.
Key terms, files and utilities : Majordomo MTA
=== Exercises ===.

## Using Postfix

Postfix is written and maintained by Wietse Venema who has also written tcp_wrappers, and Satan. Postfix began its life as VMailer but Wietse has released the software under the IBM GPL and IBM's lawyers discovered that VMailer was too similar to an existing trade mark so the name had to be changed. Postfix is written as a drop in replacement for sendmail and it comes very close to hitting the mark on this. There are a few ?gotchas? which can bite you but they are not serious. Wietse actively supports Postfix through the postfix-users mailing list and there is also a developers mailing list. You can subscribe to the postfix-users mailing list this way:
You can subscribe to the developers list in this way:
One last list we should mention is the announce list. You can join the announce list in this way: echo subscribe postfix-announce | mail majordomo@postfix.org. Postfix development is on-going and these mailing lists are quite active as of this writing. Archives for the mailing lists may be found at: http://www.egroups.com/group/postfix-users/ and at: http://msgs.SecurePoint.com/postfix/.
When a message enters the Postfix mail system, the first stop on the inside is the incoming queue. The figure below shows the main components that are involved with new mail.
The figure shows the main Postfix system components, and the main information flows between them. Yellow ellipsoids are mail programs, Yellow boxes are mail queues or files. Blue boxes are lookup tables.
Programs in the large box run under control by the Postfix resident master daemon. Data in the large box is property of the Postfix mail system.
Mail is posted locally. The Postfix sendmail program invokes the privileged postdrop program which deposits the message into the maildrop directory, where the message is picked up by the pickup daemon. This daemon does some sanity checks, in order to protect the rest of the Postfix system.
Mail comes in via the network. The Postfix SMTP server receives the message and does some sanity checks, in order to protect the rest of the Postfix system. The SMTP server can be configured to implement UCE controls on the basis of local or network-based black lists, DNS lookups, and other client request information. Mail is generated internally by the Postfix system itself, in order to return undeliverable mail to the sender. The bounce or defer daemon brings the bad news.
Mail is forwarded by the local delivery agent, either via an entry in the system-wide alias database, or via an entry in a per-user .forward file. This is indicated with the unlabeled arrow.
Mail is generated internally by the Postfix system itself, in order to notify the postmaster of a problem (this path is also indicated with the unlabeled arrow). The Postfix system can be configured to notify the postmaster of SMTP protocol problems, UCE policy violations, and so on.
The cleanup daemon implements the final processing stage for new mail. It adds missing From: and other message headers, arranges for address rewriting to the standard user@fully.qualified.domain form, and optionally extracts recipient addresses from message headers. The cleanup daemon inserts the result as a single queue file into the incoming queue, and notifies the queue manager of the arrival of new mail. The cleanup daemon can be configured to transform addresses on the basis of canonical and virtual table lookups.
On request by the cleanup daemon, the trivial-rewrite daemon rewrites addresses to the standard user@fully.qualified.domain form. The initial Postfix version does not implement a rewriting language. Implementing one would take a lot of effort, and most sites do not need it. Instead, Postfix makes extensive use of table lookup.
The primary configuration file for Postfix (the working equivalent to /etc/sendmail.cf) is main.cf. The install.cf file contains the initial settings for Postfix which were set up during the RPM installation. The file master.cf is Postfix' master process configuration file. Each line in the master file describes how a mailer component program should be run. In the debugging section we will talk some more about this file. The postfix-script is a wrapper used by Postfix to execute Postfix commands safely for the Linux environment. Let's take a closer look at the install.cf file as this file contains some data which we will need when we start to configure Postfix with main.cf.
The install.cf file is really just a list of the default settings used by the installation program built into the RPM.
Here is the main.cf file with comments by Wietse Venema and our suggested changes interspersed throughout :
This is the same directory that sendmail uses for the incoming mail queue.
The line above must be corrected. The RPM installs the Postfix binaries into /usr/libexec/postfix by default.
The line above is correct and may be left as is.
The line above is correct and may be left as is.
The line above is correct and may be left as is.
The line above is correct and may be left as is but it should be uncommented (e.g. Remove the leading pound sign).
Set the value in the line above to the Fully Qualified Domain Name (FQDN) for you machine. E.g. if your hostname is turkey and your domain is trot.com then your FQDN would be ?turkey.trot.com?. You will also need to uncomment this line.
The line above is redundant for most configurations and can usually be left commented.
The line above should be your domain name only without the hostname prepended to the front of it. As in the example we gave above the correct value here would be trot.com. Don't forget to uncomment the line as well.
The instructions here are pretty good. Typically what's done here is to let this default to $mydomain. Be sure to uncomment your choice.
Once again the instructions here are good. Just uncomment the above listed line and you should be fine. Unless you have some odd requirement the next two entries can be left commented. You shouldn't need them.
The most common practice is to select the line immediately above as your choice here. Be sure to uncomment it and put a comma between the last two entries as it appears to have been omitted.
If you are behind some sort of a firewall or you need to masquerade the envelope (which will be covered later in this document) you would set the ?relayhost? value to the MTA for your domain. If this host is to be *the* MTA for the domain then leave all of these commented out.
In most cases the above line would be uncommented and left as is.
The alias_maps line is pointing at the /etc/aliases file which we preserved prior to removing sendmail. Best practice (recommended) usually prefers that all the Postfix config files be kept together so it might be a good idea to change this line to read:
and also make sure that you put the aliases file in /etc/postfix. Otherwise Postfix will complain on startup and fail to run. The default db type on Red Hat Linux is hash so be sure and use it as we have here. One common error which people have is when they use dbm instead of hash. Don't fall into that trap.
As the instructions say if you want to use the newaliases command to handle the aliases file (recommended) you should uncomment the above line but be sure (if you made the path change we recommended in the alias_maps section) and change it to read:
Then be sure to uncomment the line and run the newaliases command before starting Postfix.
If you happen to run majordomo then you should use the line above instead of just the aliases line. Be sure the path to the file majordomo is correct. The best practice convention is to put it into /etc/postfix. Most Red Hat Linux sendmail installations would have had it in /etc/mail/. We will dicuss this a bit more when we get to the listserv section of this document.
The defaults will work fine so you can leave this section commented out unless you have some special need or preference.
This one can be left commented out also, unless you have some special need or preference.
On Red Hat Linux systems you should leave this alone unless you know what you're doing. If you're converting from qmail to Postfix (doubtful) then it would probably be useful.
The previous line is correct for Red Hat Linux defaults so it should be uncommented and left as is.
The default MDA on Red Hat Linux systems is procmail. You can use the command ?which procmail? to verify the path but unless you've changed procmail's location it is located in ?/usr/bin/procmail?. Don't forget to uncomment the line.
On a default Red Hat Linux system you should leave the above line alone.
On a default Red Hat Linux system you should leave the above line alone.
It's your choice what you do here but it can be quite annoying to receive a bazillion bounces a day. Leave this alone (recommended).
The above section enables a filter which you can use to detect and ?bounce? mail which matches a certain regular expression (REGEXP). The difference between using procmail and regexp or PCRE is that these two catch the mail prior to delivery and can effectively block unwanted mail at the SMTP port.
For anyone who knows already how MX records work this is a critical component in the Postfix configuration. Home users probably won't need this line but anyone who handles mail for mutiple domains will.
Here's a sample of how it can be used:
In this example the domains you want to relay for would be placed in the file /etc/postfix/relay-domains. One to a line like so:
Note: this file is *not* hashed or mapped. It is a simple text file. You can also use IP addresses instead of names.
The line above is another critical component in the configuration of Postfix. As the instructions say it specifies the list of networks that are local to this host. For those unfamiliar with the syntax used, it's called Classless Inter-Domain Routing (CIDR) or supernetting. For those familiar with the network classes (A, B, C etc.) it is a way of dividing IP addresses up without reference to class.
The above config entry is a matter of personal preference. It is not required and is up to the administrator to choose.
As the text above says this section is really about rate limiting. It is, essentially, the gas pedal for Postfix. Unless you have some really good reason to change these the defaults should be fine. Once you've run Postfix for a while (particularly those who use it in a professional setting) you may have a better idea of how this should be set for your environment.
We recommend the default here unless there is some overriding reason to change this. Debugging will be covered in a later chapter of this document. For what it's worth this section has no real relevance unless the next is enabled.
This section is used in combination with debug_peer_level so if that's not enabled then this one is moot. This is actually a very neat feature of Postfix. Think about it for a minut. If everything works fine but there is this one host which seems to have problem receiving or sending mail to or from your host then you could use this feature to increase the logging level for just that host.
Leave this section alone for now. We will cover debugging in some detail in a later section of this document. That's it. We've made it through the main.cf file and we're almost ready to start it up.

### master.cf

The master daemon is a supervisory application which controls and monitors all of the other Postfix processes. The master.cf file is the master daemon's configuration file. The master.cf file is the throttle for Postfix. Here you set all of the daemon process count limits. A good example of a useful limit would be to set a limit on the number of SMTP processes which can be executed simultaneously, after all, you might not want to receive 50 messages inbound all at the same time. The key thing to understand here is that any process without an express limit defaults to a 50 process limit.
In general terms the master.cf file is fine with the defaults as they are so you can leave it alone.

### aliases

This is simply the default aliases file and it could be exactly the same one you used with sendmail (recommended) and it works the same way it always has with the newaliases command. If you use majordomo your majordomo aliases will work the same way they always have and they will work with the newaliases command as well.
Control of the postfix server is done through the init.d scripts Don't forget to issue a postfix reload command after changing the configuration ! If you modify the aliases database (/etc/aliases), don't forget to activate the changes by issueing a newaliases command (as with sendmail)
Key terms, files and utilities : /etc/aliases /etc/postfix/main.cf /etc/postfix/master.cf /var/spool/postfix

### Exercises
## Managing mail trafic

procmail is the mail processing utility language written by Stephen van den Berg of Germany. This article provides a bit of background for the intermediate Unix user on how to use procmail. As a "little" language (to use the academic term) procmail lacks many of the features and constructs of traditional, general-purpose languages. It has no "while" or "for" loops. However it "knows" a lot about Unix mail delivery conventions and file/directory permissions -- and in particular about file locking. Although it is possible to write a custom mail filtering script in any programming language using the facilities installed on most Unix systems -- we'll show that procmail is the tool of choice among sysadmins and advanced Unix users.
Unix mail systems consist of MTA's (mail transport agents like sendmail, smail, qmail mmdf etc), MDA's (delivery agents like sendmail, deliver, and procmail), and MUA's (user agents like elm, pine, /bin/mail, mh, Eudora, and Pegasus).
On most Unix systems on the Internet sendmail is used as an integrated transport and delivery agent. sendmail and compatible MTA's have the ability to dispatch mail *through* a custom filter or program through either of two mechanisms: aliases and .forwards.
The aliases mechanism uses a single file (usually /etc/aliases or /usr/lib/aliases) to redirect mail. This file is owned and maintained by the system administrator. Therefore you (as a user) can't modify it. The ".forward" mechanism is decentralized. Each user on a system can create a file in their home directory named .forward and consisting of an address, a filename, or a program (filter). Usually the file *must* be owned by the user or root and *must not* be "writeable" by other users (good versions of sendmail check these factors for security reasons).
It's also possible, with some versions of sendmail, for you to specify multiple addresses, programs, or files, separated with commas. However we'll skip the details of that. Managing mail trafic
You could forward your mail through any arbitrary program with a .forward that consisted of a line like:
Note the quotes and the "pipe" character. They are required. "Your.program" could be a Bourne shell script, an awk or perl script, a compiled C program or any other sort of filter you wanted to write.
However "your.program" would have to be written to handle a plethora of details about how sendmail would pass the messages (headers and body) to it, how you would return values to sendmail, how you'd handle file locking (in case mail came in while "your.program" was still processing one, etc). That's what procmail gives us.
What we have seen so far is general information that applies to all sendmail compatible MTA/MDA's. Managing mail trafic
So, to ensure that mail is passed to procmail for processing the first step is to create the .forward file. (This is safe to do before you do any configuration of procmail itself -- assuming that the package's binaries are installed). Here's the canonical example, pasted from the procmail man pages:
If you did this and nothing else your mail would basically be unaffected. procmail would just look for its default recipe file (.procmailrc) and finding none -- it would perform its default action on each messages. In other words it would append new messages into your normal spool file.
You can setup procmail system-wide as local delivery agent in sendmail/postfix. When this is done, you can skip the whole part of about using the .forward file -- or you can use it anyway. For instance in sendmail this can be done by changing sendmail.mc with the following:
In postfix this can be done according to the postfix FAQ. Basically it is just editing /etc/postfix/main.cf with the following and reloading postfix.
In either event the next step to automating your mail handling is to create a .procmailrc file in your home directory. You could actually call this file anything you wanted -- but then you'd have to slip the name explicitly into the .forward file (right before the "||" operator). Almost everyone just uses the default.
So far all we've talked about it how everything gets routed to procmail -- which mostly involves sendmail and the Bourne shell's syntax. Almost all sendmail's are configured to use /bin/sh (the Bourne shell) to interpret alias and .forward "pipes."
So, here's a very simple .procmailrc file:
This just appends an extra copy of all incoming mail to a file named "mail.backup" in your home directory. Note that a bunch of environment variables are preset for you. It's been suggested that you should explicitly set SHELL=/bin/sh (or the closest derivative to Bourne Shell available on your system). I've never had to worry about that since the shells I use on most systems are already Bourne compatible.
However, csh and other shell users should take note that all of the procmail recipe examples that I've ever seen use Bourne syntax.
The :0 line marks the beginning of a "recipe" (procedure, clause, whatever. :0 can be followed be any of a number of "flags." There is a literally dizzying number of ways to combine these flags. The one flag we're using in this example is 'c' for "copy."
The second colon on this line marks the end of the flags and the beginning of the name for a lockfile. Since no name is given procmail will pick one automatically.
This bit is a little complicated. Mail might arrive in bursts. If a new message arrives while your script is still busy processing the last message -- you'll have multiple sendmail processes. Each will be dealing with one message. This isn't a problem by itself. However -- if the two processes might try to write into one file at the same time they are likely to get jumbled in unpredictable ways (the result will not be a properly formatted mail folder).
So we hint to procmail that it will need the check for and create a lockfile. In this particular case we don't care what the name of the lock file would be (since we're not going to have *other* programs writing into the backup file). So we leave the last field (after the colon) blank. procmail will then select its own lockfile name.
If we leave the : off of the recipe header line (omitting the last field entirely) then no lockfile is used. This is appropriate whenever we intend to only read from the files in the recipe -- or in cases where we intend to only write short, single line entries to a file in no particular order (like log file entries). The way procmail works is:
It receives a single message from sendmail (or some sendmail compatible MTA/MDA). There may be several procmail processing running currently since new messages may be coming in faster than they are being processed. It opens its recipe file (.procmailrc by default or specified on its command line) and parses each recipe from the first to the last until a message has been "delivered" (or "disposed of" as the case may be).
Any recipe can be a "disposition" or "delivery" of the message. As soon as a message is "delivered" then procmail closes its files, removes its locks and exits.
If procmail reaches the end of it's rc file (and thus all of the INCLUDE'd files) without "disposing" of the message -- than the message is appended to your spool file (which looks like a normal delivery to you and all of your "mail user agents" like Eudora, elm, etc).
This explains why procmail is so forgiving if you have *no* .procmailrc. It simply delivers your message to the spool because it has reached the end of all its recipes (there were none). The 'c' flag causes a recipe to work on a "copy" of the message -- meaning that any actions taken by that recipe are not considered to be "dispositions" of the message.
Without the 'c' flag this recipe would catch all incoming messages, and all your mail would end up in mail.backup. None of it would get into your spool file and none of the other recipes would be parsed.
The next line in this sample recipe is simply a filename. Like sendmail's aliases and .forward files -- procmail recognizes three sorts of disposition to any message. You can append it to a file, forward it to some other mail address, or filter it through a program.
Actually there is one special form of "delivery" or "disposition" that procmail handles. If you provide it with a directory name (rather than a filename) it will add the message to that directory as a separate file. The name of that file will be based on several rather complicated factors that you don't have to worry about unless you use the Rand MH system, or some other relatively obscure and "exotic" mail agent.
A procmail recipe generally consists of three parts -- a start line (:0 with some flags) some conditions (lines starting with a '*' -- asterisk -- character) and one "delivery" line which can be file/directory name or a line starting with a '!' -- bang -- character or a '|' -- pipe character.
Here's another example:
This is a simple one consisting of no flags, one condition and a simple file delivery. It simply throws away any mail from "someone I don't like." (/dev/null under Unix is a "bit bucket" -- a bottomless well for tossing unwanted output DOS has a similar concept but it's not nearly as handy).
Here's a more complex one:
This consists of a set of negative conditions (notice that the conditions all start with the '!' character). This means: for any mail that didn't come from a "daemon" (some automated process) and didn't come a "mailer" (some other automated process) and which doesn't contain any header line of the form: "X-Loop: myadd..." send it through the script in my bin directory.
I can put the script directly in the rc file (which is what most procmail users do most of the time). This script might do anything to the mail. In this case -- whatever it does had better be good because procmail way will consider any such mail to be delivered and any recipes after this will only be reached by mail from DAEMONs, MAILERs and any mail with that particular X-Loop: line in the header.
These two particular FROM_ conditions are actually "special." They are preset by procmail and actually refer to a couple of rather complicated regular expressions that are tailored to match the sorts of things that are found in the headers of most mail from daemons and mailers.
The X-Loop: line is a normal procmail condition. In the RFC822 document (which defines what e-mail headers should look like on the Internet) any line started with X- is a "custom" header. This means that any mail program that wants to can add pretty much any X- line it wants.
A common procmail idiom is to add an X-Loop: line to the header of any message that we send out -- and to check for our own X-Loop: line before sending out anything. This is to protect against "mail loops" -- situations where our mail gets forwarded or "bounced" back to us and we endlessly respond to it.
So, here's a detailed example of how to use procmail to automatically respond to mail from a particular person. We start with the recipe header.
... then we add our one condition (that the mail appears to be from the person in question):
FROM is a "magic" value for procmail -- it checks from, resent-by, and similar header lines. You could also use ^From: -- which would only match the header line(s) that start with the string "From:"
The ^ (hiccup or, more technically "caret") is a "regular expression anchor" (a techie phrase that means "it specifies *where* the pattern must be found in order to match." There is a whole book on regular expression (O'Reilly & Associates). "regexes" permeate many Unix utilities, scripting languages, and other programs. There are slight differences in "regex" syntax for each application. However the man page for 'grep' or 'egrep' is an excellent place to learn more.
In this case the hiccup means that the pattern must occur at the beginning of a line (which is its usual meaning in grep, ed/sed, awk, and other contexts).
... and we add a couple of conditions to avoid looping and to avoid responding to automated systems
(These are a couple more "magic" values. The man pages show the exact regexes that are assigned to these keywords -- if you're curious or need to tweak a special condition that is similar to one or the other of these).
... and one more to prevent some tricky loop:
(All of these patterns start with "bangs" (exclammation points) because the condition is that *no* line of the header start with any of these patterns. The 'bang' in this case (and most other regex contexts) "negates" or "reverses" the meaning of the pattern).
... now we add a "disposition" -- the autoresponse.
This is pretty complicated -- but here's how it works: The | character tells procmail that it should launch a program and feed the message to it. The open parenthesis is a Bourne shell construct that groups a set of commands in such a way as to combine the output from all of them into one "stream."
The 'formail' command is a handy program that is included with the procmail package. It "formats" mail headers according to its command line switches and its input. -rk tells 'formail' to format a "reply" and to "keep" the message body. With these switches formail expects a header and body as input.
The -A parameters tells formail to "add" the next parameter as a header line. The parameters provided to the -A switch must be enclosed in quotes so the shell treats the whole string (spaces and all) as single parameters. The backslashes at the end of each line tell procmail mail to treat the next line as part of this one. So, all of the lines ending in backslashes are passed to the shell as one long line.
This "trailing backslash" or "line continuation" character is a common Unix idiom found in a number of programming languages and configuration file formats. The semicolons tell the shell to execute another command -- they allow several commands to be issued on the same command line.
Each of the echo commands should be reasonably self-explanatory. We could have used a 'cat' command and put our text into a file if we wanted. We can also call other programs here -- like 'fortune' or 'date' and their output would be combined with the rest of this).
Now we get to the closing parenthesis. This marks the end of the block of commands that we combined. The output from all of those is fed into the next pipe -- which starts the local copy of sendmail (note that this is another variable that procmail toughtfully presets for us).
The -t switch on sendmail tell it to take the "To:" address from the header of it's input (where 'formail -r' put it) and the -oi switch enables the sendmail "option" to "ignore" lines that consist only of a 'dot' (don't worry about the details on that).
Most of the difficulty in understanding procmail as nothing to do with procmail itself. The intricacies of regular expressions (those wierd things on the '*' -- conditional lines) and shell quoting and command syntax, and how to format a reply header that will be acceptable to sendmail (the 'formail' and 'sendmail' stuff) are the parts that require so much explanation.
More information about procmail can be found in Era Eriksson's "Mini-FAQ." at http://www.iki.fi/~era/procmail/mini-faq.html or one of the several mirrors like http://www.zer0.org/procmail/mini-faq.html http://www.dcs.ed.ac.uk/home/procmail/faq/mini-faq.html
Key terms, files and utilities : Procmail .procmailrc
=== Exercises ===.

## Serving news

The INND daemon is one of the most used news server program It provides Network News Transport Protocol (NNTP) service. Major newsgroups include: alt,comp,gnu,misc,news,rec,sci,soc, and talk. Newsgroups are configured in a hierarchical fashion. INND by default uses the NNTP port TCP 119
Configuration :
Location of configuration files is /etc/news/. A minimal leafnode setup requires that you modify the following files:
inn.conf :
Set the following options. The defaults for the remaining options should be fine.
Place your ISP's news server information in here.

### Newsfeeds

If you want to post articles, you need to modify newsfeeds. news.myisp.com:comp.*,!comp.sources.*,comp.sources.unix/!foo:Tf,Wnm:news.myisp.com The colon is the field delimiter used above. The format of that above line is: sitename[/exclude,exclude,...]:pattern,pattern,...[/distrib,distrib,..]:flag,flag,...:param
Options:

#### sitename

    Names the site to which this feed relates. It can be called anything you want and does not have to be the domain name of the site.

#### pattern

    Indicates which news groups are to be sent to this site. The default is to send all groups (leave it blank if that's what you want). The above example will cause all "comp" groups to be received, but not any group under "comp.sources" except for "comp.sources.unix".

#### distribution

    If specified, and an article has a "Distribution" header, it is check against this value. If the distribution specified matches the distribution header in the article, it is sent. However, if the distribution specified starts with an exclamation point, and the distribution header in the article matches, it is not sent. In the above example, any article with a distribution header containing "foo" will not be sent.

#### flag

    Specify various options about the newsfeed. The above options specify that this is a file feed type (Tf), and that only articles "message-id" and "token" (Wmn) should be written.
param - Meaning varies depending on the feed type. When the feed type is "file" as in the example above, it specifies the file to write an entry to when an article is received. If not an absolute path, it is relative to the "pathoutgoing" option in inn.conf.
readers.conf : Edit this file if you want to allow readers on other computers. motd.news : if you allow readers, it is a good idea to put a banner in this file that relays your usage policies to your readers.
Run inncheck to correct any permissions problems and catch any configuration file errors. Run makehistory to initialize the INN history database. Run makedbz to rebuild the dbz database files. Run innd and test with a news client

### Troubleshooting

innd won't start Use inncheck. Check logs under /var/log/news. Readers can't read : Verify that the reader is allowed access by checking nnrp.access. Make sure innd is running. Check logs under /var/log/news. telnet to port 119 and see if a banner comes up. Posters can't post : Confirm poster is allowed to post by checking nnrp.access. Check logs under /var/log/news. telnet to port 119 and see if a banner comes up with (posting allowed).
Key terms, files and utilities : Innd