Table of Contents Previous Chapter Electronic Mail.
A few years ago, electronic mail (email) was a new thing that was mostly used by computer nerds. Today, if mail is broken on our machines, the secretaries are the first to complain; almost all departmental communication is done by electronic mail rather than by telephone, memos, or discussions.
The transport agent is responsible for actually receiving and delivering messages. It should:
The original mail agent. Ugly. Don't use it if you have a better mailer.
The Berkeley mail agent. This is still popular, even if a little crude. The file format is widely used be other mailers. Most users will prefer a friendlier interface.
- Sun's mailtool
This mail agent is only found on Suns. It has a GUI front end that uses standard Berkeley mail format.
This public domain mail agent is powerful and easy to use. It uses the standard Unix editors (vi, emacs or even pico). It is compatible with Berkeley mail. Newest version supports MIME. (The elm mailer is not supported by C&C)
A highly customizable and programmable mailer that is "unbundled" so that it can be used while doing other work (i.e., it is not a single program, but instead many small simple programs). The xmh program provides a GUI for email on systems that support the X Window System.
A slick but very simple mail agent. It was designed to be usable by a novice user but is sophisticated enough for experts. Developed by University of Washington software engineers, it is distributed world-wide. It can be ported to almost any Unix system. Can run on any terminal that does VT100 emulation. The pine mailer is supported on all Uniform Access hosts by C&C.
It makes use of the full screen, perhaps at a cost for modem users, and can make use of function keys when used with NCSA telnet. It has it's own built in editor and browser that can't be substituted by any of the usual UNIX editors and browsers, and it pays little attention to any environment variables.
The pine mailer also acts as an IMAP client for multi-host mail reading.
Features of the pine mailer.
- View, save, delete, print, reply and forward messages
- Compose message in a simple editor with word wrap
- Temporarily suspend composing one message so another can be viewed or composed
- Mail folders for saving mail which can selected from an on screen list
- Address book to keep a list of long or frequently used addressed (can be taken from incoming mail without retyping)
- Automatic notification and incorporation of new mail
- On line context sensitive help screens
- Show disk space used by mail folders, and free space on the disk
The predominant mail transport agent on Unix systems is sendmail.
- Accept messages from the user agent
- Understand destination addresses
- Deliver mail originating on the local machine to the proper mailbox[es] if local, or to a delivery agent if remote
- Receive incoming mail from other delivery agents and deliver to local users
The configuration file (/usr/lib/sendmail.cf) is organized into three broad sections:
sendmail allows the system administrator to define symbols, classes, options, priorities, and many other configuration parameters for mail delivery. The commands to do this usually precede the meat of the configuration file, the address rewriting rules. This is nice, since they are relatively easy to understand and give someone new to the config file a healthy dose of overconfidence.
- Definitions of symbols, classes, options and parameters
- Address rewriting rules
- Definitions of mailers and delivery programs, and how to invoke them
Configuration of sendmail is somewhat of a "Black Art." It is a very complex mail delivery agent that is designed to handle several mail transport mechanisms, address format translations, and delivery options. Each vendor will include enhancements for their own specific Unix implementations.
You can find the latest version of sendmail used by C&C at ftp://ftp.cac.washington.edu/mail/sendmail, There are also several example configuration files there. For documentation on configuration of sendmail, refer to "sendmail" by Bryan Costales, Eric Allman, and Neil Rickert.
If at all possible, use the Uniform Access hosts for email, or use an IMAP client (e.g., pine, PC pine, or MailStrom) from a Uniform Access IMAP server.
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