Contributed by &a.wlloyd;.

E-mail, as simple as the concept sounds, can be extremely complicated. If you plan on doing anything beyond setting up a simple one machine E-mail system, you should buy and refer to a book on Sendmail. Introduction

These are the major programs or components of an e-mail exchange. User program

This is a program like sendmail or delivering it over TCP to your mailhost. Transport Agent - Sendmail

Usually this program is /etc/sysconfig . It is best to leave it on unless you have a specific reason to want it off. Ie: Firewall

You should be aware that sendmail is a potential weak link in a secure site. Some versions of sendmail have known security problems.

sendmail will look up in the DNS to determine the actual host that will receive mail for the destination.

Sendmail will take the message from the local queue and deliver it across the Internet to another sendmail on the receivers computer.

Sendmail will also be able to do the reverse. It will accept messages and save them on your local machine. POP Servers

This program gets the mail from your mailbox and gives it to your browser. If you want to run a POP server on your computer, you will need to do 2 things. Get pop software from the ports or packages collection. Modify /etc/inetd.conf to load POP server. The pop program you get will have instructions with it. Read them. Configuration

As your FreeBSD system comes "out of the box" you should be able to send e-mail to external hosts. The problem is no mail will be able to get back to your host. This is not a problem if you are willing to make sure you hand edit the automatic reply to address every time you send a message.

It is relatively simple to get another host to receive your e-mail under the same username. You can then pick it up over POP or telnet. A user account with the SAME USERNAME should exist on both machines. Please use /nonexistent the user will not be allowed to login. The mailhost that you will be using must be designated the Mail exchange for your host. This must be arranged in DNS (ie BIND, named). Please refer to a Networking book for more information. You basically need to add these lines in your DNS server. myhost.smalliap.com A xxx.xxx.xxx.xxx ; Your ip MX 10 smtp.smalliap.com ; your mailhost You cannot do this yourself unless you are running a DNS server. If you do not want to run a DNS server, get somebody else like your Internet Provider to do it. This will redirect mail for your host to the MX (Mail eXchange) host. It does not matter what machine the A record points to, the mail will be sent to the MX host.

This feature is used to implement Virtual Hosting.

Example

I have a customer with domain foo.bar and I want all mail for foo.bar to be sent to my machine smtp.smalliap.com. You must make an entry in your DNS server like: foo.bar MX 10 smtp.smalliap.com ; your mailhost The A record is not needed if you only want e-mail for the domain. On the mailhost that actually accepts mail for final delivery to a mailbox, sendmail must be told what hosts it will be accepting mail for.

Add myhost.smalliap.com to /etc/sendmail.cw (if you are using FEATURE(use_cw_file)), or add a "Cw myhost.smalliap.com" line to /etc/sendmail.cf.

To actually receive mail on your host, you need to have the MX entry above changed to point to your host. You also move the Cw line above in your sendmail.cf.

This is a Bad Idea if your connection to the Internet is not permanent. Mail will bounce.

If you plan on doing anything serious with . FAQ Why do I have to use the FQDN for hosts on my site?

You will probably find that the host is actually in a different domain; for example, if you are in foo.bar.edu and you wish to reach a host called ``mumble'' in the bar.edu domain, you will have to refer to it by the fully-qualified domain name, ``mumble.bar.edu'', instead of just ``mumble''.

Traditionally, this was allowed by BSD BIND resolvers. However the current version of BIND that ships with FreeBSD no longer provides default abbreviations for non-fully qualified domain names other than the domain you are in. So an unqualified host mumble must either be found as mumble.foo.bar.edu, or it will be searched for in the root domain.

This is different from the previous behavior, where the search continued across mumble.bar.edu, and mumble.edu. Have a look at RFC 1535 for why this was considered bad practice, or even a security hole.

As a good workaround, you can place the line

search foo.bar.edu bar.edu

instead of the previous

domain foo.bar.edu

into your /etc/resolv.conf. However, make sure that the search order does not go beyond the ``boundary between local and public administration'', as RFC 1535 calls it. Sendmail says ``mail loops back to myself''

This is answered in the sendmail FAQ as follows:- * I'm getting "Local configuration error" messages, such as: 553 relay.domain.net config error: mail loops back to myself 554 ... Local configuration error How can I solve this problem? You have asked mail to the domain (e.g., domain.net) to be forwarded to a specific host (in this case, relay.domain.net) by using an MX record, but the relay machine doesn't recognize itself as domain.net. Add domain.net to /etc/sendmail.cw (if you are using FEATURE(use_cw_file)) or add "Cw domain.net" to /etc/sendmail.cf.

The sendmail FAQ is in /usr/src/usr.sbin/sendmail and is recommended reading if you want to do any ``tweaking'' of your mail setup. How do I use sendmail for mail delivery with UUCP?

The sendmail configuration that ships with FreeBSD is suited for sites that connect directly to the Internet. Sites that wish to exchange their mail via UUCP must install another sendmail configuration file.

Tweaking /etc/sendmail.cf manually is considered something for purists. Sendmail version 8 comes with a new approach of generating config files via some m4 preprocessing, where the actual hand-crafted configuration is on a higher abstraction level. You should use the configuration files under /usr/src/usr.sbin/sendmail/cf If you did not install your system with full sources, the sendmail config stuff has been broken out into a separate source distribution tarball just for you. Assuming you have your CD-ROM mounted, do: cd /usr/src tar -xvzf /cdrom/dists/src/ssmailcf.aa Do not panic, this is only a few hundred kilobytes in size. The file README in the cf directory can serve as a basic introduction to m4 configuration.

For UUCP delivery, you are best advised to use the mailertable feature. This constitutes a database that sendmail can use to base its routing decision upon.

First, you have to create your .mc file. The directory /usr/src/usr.sbin/sendmail/cf/cf is the home of these files. Look around, there are already a few examples. Assuming you have named your file foo.mc, all you need to do in order to convert it into a valid sendmail.cf is: cd /usr/src/usr.sbin/sendmail/cf/cf make foo.cf cp foo.cf /etc/sendmail.cf A typical .mc file might look like: include(`../m4/cf.m4') VERSIONID(`Your version number') OSTYPE(bsd4.4) FEATURE(nodns) FEATURE(nocanonify) FEATURE(mailertable) define(`UUCP_RELAY', your.uucp.relay) define(`UUCP_MAX_SIZE', 200000) MAILER(local) MAILER(smtp) MAILER(uucp) Cw your.alias.host.name Cw youruucpnodename.UUCP The nodns and nocanonify features will prevent any usage of the DNS during mail delivery. The UUCP_RELAY clause is needed for bizarre reasons, do not ask. Simply put an Internet hostname there that is able to handle .UUCP pseudo-domain addresses; most likely, you will enter the mail relay of your ISP there.

Once you have this, you need this file called /etc/mailertable. A typical example of this gender again: # # makemap hash /etc/mailertable.db < /etc/mailertable # horus.interface-business.de uucp-dom:horus .interface-business.de uucp-dom:if-bus interface-business.de uucp-dom:if-bus .heep.sax.de smtp8:%1 horus.UUCP uucp-dom:horus if-bus.UUCP uucp-dom:if-bus . uucp-dom:sax As you can see, this is part of a real-life file. The first three lines handle special cases where domain-addressed mail should not be sent out to the default route, but instead to some UUCP neighbor in order to ``shortcut'' the delivery path. The next line handles mail to the local Ethernet domain that can be delivered using SMTP. Finally, the UUCP neighbors are mentioned in the .UUCP pseudo-domain notation, to allow for a ``uucp-neighbor!recipient'' override of the default rules. The last line is always a single dot, matching everything else, with UUCP delivery to a UUCP neighbor that serves as your universal mail gateway to the world. All of the node names behind the uucp-dom: keyword must be valid UUCP neighbors, as you can verify using the command uuname.

As a reminder that this file needs to be converted into a DBM database file before being usable, the command line to accomplish this is best placed as a comment at the top of the mailertable. You always have to execute this command each time you change your mailertable.

Final hint: if you are uncertain whether some particular mail routing would work, remember the -bt option to sendmail. It starts sendmail in address test mode; simply enter ``0 '', followed by the address you wish to test for the mail routing. The last line tells you the used internal mail agent, the destination host this agent will be called with, and the (possibly translated) address. Leave this mode by typing Control-D. j@uriah 191% sendmail -bt ADDRESS TEST MODE (ruleset 3 NOT automatically invoked) Enter