Reading Mail with Rmail
***********************

Rmail is an Emacs subsystem for reading and disposing of mail that you receive.  Rmail stores mail messages in files called Rmail files. Reading the message in an Rmail file is done in a special major mode, Rmail mode, which redefines most letters to run commands for managing mail.  To enter Rmail, type M-x rmail.  This reads your primary mail file, merges new mail in from your inboxes, displays the first message you haven't read yet, and lets you begin reading.

Using Rmail in the simplest fashion, you have one Rmail file ~/RMAIL in which all of your mail is saved.  It is called your primary mail file.  In more sophisticated usage, you can copy messages into other Rmail files and then edit those files with Rmail.

Rmail uses narrowing to hide all but one message in the Rmail file. The message that is shown is called the current message.  Rmail mode's special commands can do such things as delete the current message, copy into another file, send a reply, or move to another message.

Within the Rmail file, messages are arranged sequentially in order of receipt.  They are also assigned consecutive integers as their message numbers.  The number of the current message is displayed in Rmail's mode line, followed by the total number of messages in the file.  You can move to a message by specifying its message number using the j key (see Rmail Motion).

Following the usual conventions of Emacs, changes in an Rmail file become permanent only when the file is saved.  You can do this with s (rmail-save), which also expunges deleted messages from the file first (see Rmail Deletion).  To save the file without expunging, use C-x C-s.  Rmail saves the Rmail file spontaneously when moving new mail from an inbox file (see Rmail Inbox).

You can exit Rmail with q (rmail-quit); this expunges and saves the Rmail file and then switches to another buffer.  But there is no need to `exit' formally.  If you switch from Rmail to editing in other buffers, and never happen to switch back, you have exited.  (The Rmail command b, rmail-bury, does this for you.)  Just make sure to save the Rmail file eventually (like any other file you have changed).  C-x s is a good enough way to do this (see Saving).

Scrolling Within a Message
==========================

When Rmail displays a message that does not fit on the screen, it is necessary to scroll through it.  This could be done with C-v, M-v and M-<, but in Rmail scrolling is so frequent that it deserves to be easier to type.

SPC
     Scroll forward (scroll-up).

DEL
     Scroll backward (scroll-down).

.
     Scroll to start of message (rmail-beginning-of-message).

Since the most common thing to do while reading a message is to scroll through it by screenfuls, Rmail makes SPC and DEL synonyms of C-v (scroll-up) and M-v (scroll-down)

The command . (rmail-beginning-of-message) scrolls back to the beginning of the selected message.  This is not quite the same as M-<: for one thing, it does not set the mark; for another, it resets the buffer boundaries to the current message if you have changed them.

Moving Among Messages
=====================

The most basic thing to do with a message is to read it.  The way to do this in Rmail is to make the message current.  The usual practice is to move sequentially through the file, since this is the order of receipt of messages.  When you enter Rmail, you are positioned at the first message that you have not yet made current (that is, the first one that has the unseen attribute; see Rmail Labels).  Move forward to see the other new messages; move backward to reexamine old messages.

n
     Move to the next nondeleted message, skipping any intervening deleted

     messages (rmail-next-undeleted-message).

p
     Move to the previous nondeleted message

     (rmail-previous-undeleted-message).

M-n
     Move to the next message, including deleted messages (rmail-next-message).

M-p
     Move to the previous message, including deleted messages (rmail-previous-message).

j
     Move to the first message.  With argument N, move to message number N (rmail-show-message).

>
     Move to the last message (rmail-last-message).

<
     Move to the first message (rmail-first-message).

M-s REGEXP RET
     Move to the next message containing a match for REGEXP (rmail-search).

- M-s REGEXP RET
     Move to the previous message containing a match for REGEXP.

n and p are the usual way of moving among messages in Rmail.  They move through the messages sequentially, but skip over deleted messages, which is usually what you want to do.  Their command definitions are named rmail-next-undeleted-message and rmail-previous-undeleted-message.  If you do not want to skip deleted messages---for example, if you want to move to a message to undelete it---use the variants M-n and M-p (rmail-next-message and rmail-previous-message).  A numeric argument to any of these commands serves as a repeat count.

In Rmail, you can specify a numeric argument by typing just the digits.  You don't need to type C-u first.

The M-s (rmail-search) command is Rmail's version of search.  The usual incremental search command C-s works in Rmail, but it searches only within the current message.  The purpose of M-s is to search for another message.  It reads a regular expression (see Regexps) nonincrementally, then searches starting at the beginning of the following message for a match.  The message containing the match is selected.

If REGEXP is empty, M-s reuses the regexp used the previous time.

To search backward in the file for another message, give M-s a negative argument.  In Rmail you can do this with - M-s.

It is also possible to search for a message based on labels. See Rmail Labels.

To move to a message specified by absolute message number, use j (rmail-show-message) with the message number as argument.  With no argument, j selects the first message.  > (rmail-last-message) selects the last message.  < (rmail-first-message) selects the first message.

Deleting Messages
=================

When you no longer need to keep a message, you can delete it.  This flags it as ignorable, and some Rmail commands pretend it is no longer present; but it still has its place in the Rmail file, and still has its message number.

Expunging the Rmail file actually removes the deleted messages. The remaining messages are renumbered consecutively.  Expunging is the only action that changes the message number of any message, except for undigestifying (see Rmail Digest).

d
     Delete the current message, and move to the next nondeleted message (rmail-delete-forward).

C-d
     Delete the current message, and move to the previous nondeleted message (rmail-delete-backward).

u
     Undelete the current message, or move back to a deleted message and undelete it (rmail-undelete-previous-message).

x
     Expunge the Rmail file (rmail-expunge).

There are two Rmail commands for deleting messages.  Both delete the current message and select another message.  d (rmail-delete-forward) moves to the following message, skipping messages already deleted, while C-d (rmail-delete-backward) moves to the previous nondeleted message. If there is no nondeleted message to move to in the specified direction, the message that was just deleted remains current.

To make all the deleted messages finally vanish from the Rmail file, type x (rmail-expunge).  Until you do this, you can still undelete the deleted messages.

To undelete, type u (rmail-undelete-previous-message), which is designed to cancel the effect of a d command (usually).  It undeletes the current message if the current message is deleted.  Otherwise it moves backward to previous messages until a deleted message is found, and undeletes that message.

You can usually undo a d with a u because the u moves back to and undeletes the message that the d deleted.  But this does not work when the d skips a few already-deleted messages that follow the message being deleted; then the u command undeletes the last of the messages that were skipped.  There is no clean way to avoid this problem.  However, by repeating the u command, you can eventually get back to the message that you intend to undelete.  You can also select a particular deleted message with M-p command, then type u to undelete it.

A deleted message has the deleted attribute, and as a result deleted appears in the mode line when the current message is deleted.  In fact, deleting or undeleting a message is nothing more than adding or removing this attribute.  See Rmail Labels.

Rmail Files and Inboxes
=======================

Unix places incoming mail for you in a file that we call your inbox.  When you start up Rmail, it copies the new messages from your inbox into your primary mail file, an Rmail file, which also contains other messages saved from previous Rmail sessions.  It is in this file that you actually read the mail with Rmail.  This operation is called getting new mail.  It can be repeated at any time using the g key in Rmail.  The inbox file name is /usr/spool/mail/USERNAME on some systems (typically Berkeley-derived ones) and /usr/mail/USERNAME on other systems.

There are three reason for having separate Rmail files and inboxes.

 1. The inbox file format varies between operating systems and according to the other mail software in use.  Only one part of Rmail needs to know about the alternatives, and it need only understand how to convert all of them to Rmail's own format.

 2. The inbox file format usually doesn't provide a place for all the information that Rmail records.

 3. It is very cumbersome to access an inbox file without danger of losing mail, because it is necessary to interlock with mail delivery. Moreover, different operating systems use different interlocking techniques.  The strategy of moving mail out of the inbox once and for all into a separate Rmail file avoids the need for interlocking in all the rest of Rmail, since only Rmail operates on the Rmail file.

When getting new mail, Rmail first copies the new mail from the inbox file to the Rmail file; then it saves the Rmail file; then it truncates the inbox file.  This way, a system crash may cause duplication of mail between the inbox and the Rmail file, but cannot lose mail.

Copying mail from an inbox in the system's mailer directory actually puts it in an intermediate file ~/.newmail.  This is because the interlocking is done by a C program that copies to another file. ~/.newmail is deleted after mail merging is successful.  If there is a crash at the wrong time, this file continues to exist and will be used as an inbox the next time you get new mail.

Multiple Mail Files
===================

Rmail operates by default on your primary mail file, which is named ~/RMAIL and receives your incoming mail from your system inbox file. But you can also have other mail files and edit them with Rmail.  These files can receive mail through their own inboxes, or you can move messages into them with explicit Rmail commands (see Rmail Output).

i FILE RET
     Read FILE into Emacs and run Rmail on it (rmail-input).

M-x set-rmail-inbox-list RET FILES RET
     Specify inbox file names for current Rmail file to get mail from.

g
     Merge new mail from current Rmail file's inboxes (rmail-get-new-mail).

C-u g FILE RET
     Merge new mail from inbox file FILE.

To run Rmail on a file other than your primary mail file, you may use the i (rmail-input) command in Rmail.  This visits the file, puts it in Rmail mode, and then gets new mail from the file's inboxes if any.  The file should be in Rmail format.  You can use M-x rmail-input even when not in Rmail.

The file you read with i should usually be a valid Rmail file. If it is not, then Rmail tries to decompose it into a stream of messages in various known formats.  If it succeeds, it converts the whole file to an Rmail file.

Each Rmail file can contain a list of inbox file names; you can specify this list with M-x set-rmail-inbox-list RET FILES RET.  The argument can contain any number of file names, separated by commas.  It can also be empty, which specifies that this file should have no inboxes.  Once a list of inboxes is specified, the Rmail file remembers it permanently until it is explicitly changed.

If an Rmail file has inboxes, new mail is merged in from the inboxes when the Rmail file is brought into Rmail, and when you use the g (rmail-get-new-mail) command.  If the Rmail file specifies no inboxes, then no new mail is merged in at these times.  As a special exception, if your primary mail file does not specify any inbox files, it uses the standard system inbox.

To merge mail from a file that is not the usual inbox, give the g key a numeric argument, as in C-u g.  Then it reads a file name and merges mail from that file.  The inbox file is not deleted or changed in any way when g with an argument is used.  This is, therefore, a general way of merging one file of messages into another.

Copying Messages Out to Files
=============================

o FILE RET
     Append a copy of the current message to the file FILE, writing it in Rmail file format (rmail-output-to-rmail-file).

C-o FILE RET
     Append a copy of the current message to the file FILE, writing it in Unix mail file format (rmail-output).

If an Rmail file has no inboxes, the only way messages get into it is by means of explicit o commands.

o (rmail-output-to-rmail-file) appends the current message in Rmail format to the end of the specified file.  This is the best command to use to move messages between Rmail files.  If the other Rmail file is currently visited, the copying is done into the other file's Emacs buffer instead.  You should eventually save it on disk.

The C-o (rmail-output) command in Rmail appends a copy of the current message to a specified file, in Unix mail file format.  This is useful for moving messages into files to be read by other mail processors that do not understand Rmail format.

Copying a message with o or C-o gives the original copy of the message the filed attribute, so that filed appears in the mode line when such a message is current.  If you like to keep just a single copy of every mail message, set the variable rmail-delete-after-output to t; then the o and C-o commands delete the original message after copying it. (You can undelete the original afterward.)

The variable rmail-output-file-alist lets you specify intelligent defaults for the output file, based on the contents of the current message.  The value should be a list whose elements have this form:

     (REGEXP . FILENAME)

If there's a match for REGEXP in the current message, then the default file name for output is FILENAME.  If multiple elements match the message, the first matching element decides the default file name.

Normally you should use only o to output messages to other Rmail files, never C-o.  But it is also safe if you always use C-o, never o.  When a file is visited in Rmail, the last message is checked, and if it is in Unix format, the entire file is scanned and all Unix-format messages are converted to Rmail format.  (The reason for checking the last message is that scanning the file is slow and most Rmail files have only Rmail format messages.)  If you use C-o consistently, the last message is sure to be in Unix format, so Rmail will convert all messages properly.

The case where you might want to use C-o always, instead of o always, is when you or other users want to append mail to the same file from other mail processors.  Other mail processors probably do not know Rmail format but do know Unix format.

In any case, always use o to add to an Rmail file that is being visited in Rmail.  Adding messages with C-o to the actual disk file will trigger a ``simultaneous editing'' warning when you ask to save the Emacs buffer.  The messages you added to the file will then be lost if you do save the buffer.

Labels
======

Each message can have various labels assigned to it as a means of classification.  A label has a name; different names mean different labels. Any given label is either present or absent on a particular message.  A few label names have standard meanings and are given to messages automatically by Rmail when appropriate; these special labels are called attributes. All other labels are assigned only by users.

a LABEL RET
     Assign the label LABEL to the current message (rmail-add-label).

k LABEL RET
     Remove the label LABEL from the current message (rmail-kill-label).

C-M-n LABELS RET
     Move to the next message that has one of the labels LABELS (rmail-next-labeled-message).

C-M-p LABELS RET
     Move to the previous message that has one of the labels LABELS (rmail-previous-labeled-message).

C-M-l LABELS RET
     Make a summary of all messages containing any of the labels LABELS (rmail-summary-by-labels).

Specifying an empty string for one these commands means to use the last label specified for any of these commands.

The a (rmail-add-label) and k (rmail-kill-label) commands allow you to assign or remove any label on the current message.  If the LABEL argument is empty, it means to assign or remove the same label most recently assigned or removed.

Once you have given messages labels to classify them as you wish, there are two ways to use the labels: in moving and in summaries.

The command C-M-n LABELS RET (rmail-next-labeled-message) moves to the next message that has one of the labels LABELS.  The argument LABELS specifies one or more label names, separated by commas.  C-M-p (rmail-previous-labeled-message) is similar, but moves backwards to previous messages.  A preceding numeric argument to either one serves as a repeat count.

The command C-M-l LABELS RET (rmail-summary-by-labels) displays a summary containing only the messages that have at least one of a specified set of messages.  The argument LABELS is one or more label names, separated by commas. See Rmail Summary, for information on summaries.

If the LABELS argument to C-M-n, C-M-p or C-M-l is empty, it means to use the last set of labels specified for any of these commands.

Some labels such as deleted and filed have built-in meanings and are assigned to or removed from messages automatically at appropriate times; these labels are called attributes.  Here is a list of Rmail attributes:

unseen
     Means the message has never been current.  Assigned to messages when they come from an inbox file, and removed when a message is made current.  When you start Rmail, it initially shows the first message that has this attribute.

deleted
     Means the message is deleted.  Assigned by deletion commands and removed by undeletion commands (see Rmail Deletion).

filed
     Means the message has been copied to some other file.  Assigned by the file output commands (see Rmail Files).

answered
     Means you have mailed an answer to the message.  Assigned by the r command (rmail-reply).  See Rmail Reply.

forwarded
     Means you have forwarded the message to other users.  Assigned by the f command (rmail-forward).  See Rmail Reply.

edited
     Means you have edited the text of the message within Rmail. See Rmail Editing.

resent
     Means you have resent the message to other users.  Assigned by the command M-x rmail-resend.  See Rmail Reply.

All other labels are assigned or removed only by the user, and have no standard meaning.

Sending Replies
===============

Rmail has several commands that use Mail mode to send outgoing mail. See Sending Mail, for information on using Mail mode.  What are documented here are the special commands of Rmail for entering Mail mode. Note that the usual keys for sending mail, C-x m and C-x 4 m, are available in Rmail mode and work just as they usually do.

m
     Send a message (rmail-mail).

c
     Continue editing already started outgoing message
     (rmail-continue).

r
     Send a reply to the current Rmail message (rmail-reply).

f
     Forward current message to other users (rmail-forward).

C-u f
     Resend the current message to other users (rmail-resend).

M-m
     Try sending a bounced message a second time (rmail-retry-failure).

The most common reason to send a message while in Rmail is to reply to the message you are reading.  To do this, type r (rmail-reply).  This displays the *mail* buffer in another window, much like C-x 4 m, but preinitializes the Subject, To, CC and In-reply-to header fields based on the message you are replying to.  The To field is starts out as the address of the person who sent the message you received, and the CC field starts out with all the other recipients of that message.

You can exclude certain recipients from being placed automatically in the CC, using the variable rmail-dont-reply-to-names.  Its value should be a regular expression (as a string); any recipient that the regular expression matches, is excluded from the CC field. The default value matches your own name, and any name starting with info-.  (Those names are excluded because there is a convention of using them for large mailing lists to broadcast announcements.)

To omit the CC field completely for a particular reply, enter the reply command with a prefix argument: C-u r.

Once the *mail* buffer has been initialized, editing and sending the mail goes as usual (see Sending Mail).  You can edit the presupplied header fields if they are not right for you.  You can also use the commands of Mail mode, including C-c C-y to yank in the message that you are replying to, and C-c C-q to fill what was thus yanked.  You can also switch to the Rmail buffer, select a different message, switch back, and yank the new current message.

Sometimes a message does not reach its destination.  Mailers usually send the failed message back to you, enclosed in a failure message.  The Rmail command M-m (rmail-retry-failure) prepares to send the same message a second time: it sets up a *mail* buffer with the same text and header fields as before.  If you type C-c C-c right away, you send the message again exactly the same as the first time.  Alternatively, you can edit the text or headers and then send it.

Another frequent reason to send mail in Rmail is to forward the current message to other users.  f (rmail-forward) makes this easy by preinitializing the *mail* buffer with the current message as the text, and a subject designating a forwarded message.  All you have to do is fill in the recipients and send.  When you forward a message, recipients get a message which is ``from'' you, and which has the original message in its contents.

Resending is an alternative similar to forwarding; the difference is that resending sends a message that is ``from'' the original sender, just as it reached you---with a few added header fields Resent-from and Resent-to to indicate that it came via you.  To resend a message in Rmail, use C-u f.  (f runs rmail-forward, which is programmed to invoke rmail-resend if you provide a numeric argument.)

The m (rmail-mail) command is used to start editing an outgoing message that is not a reply.  It leaves the header fields empty. Its only difference from C-x 4 m is that it makes the Rmail buffer accessible for C-c C-y, just as r does.  Thus, m can be used to reply to or forward a message; it can do anything r or f can do.

The c (rmail-continue) command resumes editing the *mail* buffer, to finish editing an outgoing message you were already composing, or to alter a message you have sent.

Summaries
=========

A summary is a buffer containing one line per message to give you an overview of the mail in an Rmail file.  Each line shows the message number, the sender, the labels, and the subject.  When the summary buffer is selected, you can use almost all Rmail commands; these apply to the message described by the current line of the summary.  Moving point in the summary buffer selects messages as you move to their summary lines.

A summary buffer applies to a single Rmail file only; if you are editing multiple Rmail files, each one has its own summary buffer (if you have asked for one).  The summary buffer name is made by appending -summary to the Rmail buffer's name.  Normally only one summary buffer is displayed at a time.

Making Summaries
----------------

Here are the commands to create a summary for the current Rmail file. Once the Rmail file has a summary buffer, changes in the Rmail file (such as deleting or expunging messages, and getting new mail) automatically update the summary.

h
C-M-h
     Summarize all messages (rmail-summary).

l LABELS RET
C-M-l LABELS RET
     Summarize message that have one or more of the specified labels (rmail-summary-by-labels).

C-M-r RCPTS RET
     Summarize messages that have one or more of the specified recipients (rmail-summary-by-recipients).

C-M-t TOPIC RET
     Summarize messages that have a match for the specified regexp TOPIC in their subjects (rmail-summary-by-topic).

The h or C-M-h (rmail-summary) command fills the summary buffer for the current Rmail file with a summary of all the messages in the file. It then displays and selects the summary buffer in another window.

C-M-l LABELS RET (rmail-summary-by-labels) makes a partial summary mentioning only the messages that have one or more of the labels LABELS.  LABELS should contain label names separated by commas.

C-M-r RCPTS RET (rmail-summary-by-recipients) makes a partial summary mentioning only the messages that have one or more of the recipients RCPTS.  RCPTS should contain mailing addresses separated by commas.

C-M-t TOPIC RET (rmail-summary-by-topic) makes a partial summary mentioning only the messages whose subjects have a match for the regular expression TOPIC.

Note that there is only one summary buffer for any Rmail file; making one kind of summary discards any previously made summary.

Editing in Summaries
--------------------

You can use the Rmail summary buffer to do almost anything you can do in the Rmail buffer itself.  In fact, once you have a summary buffer, there's no need to switch back to the Rmail buffer.

You can select and display various messages in the Rmail buffer, from the summary buffer, just by moving point in the summary buffer to different lines.  It doesn't matter what Emacs command you use to move point; whichever line point is on at the end of the command, that message is selected in the Rmail buffer.

Almost all Rmail commands work in the summary buffer as well as in the Rmail buffer.  Thus, d in the summary buffer deletes the current message, u undeletes, and x expunges.  o and C-o output the current message to a file; r starts a reply to it.  You can scroll the current message while remaining in the summary buffer using SPC and DEL.

The Rmail commands to move between messages also work in the summary buffer, but with a twist: they move through the set of messages included in the summary.  They also redisplay the Rmail buffer on the screen (unlike cursor motion commands, which update the contents of the Rmail buffer but don't display it in a window unless it already appears). Here is a list of these commands:

n
     Move to next line, skipping lines saying `deleted', and select its message.

p
     Move to previous line, skipping lines saying `deleted', and select its message.

M-n
     Move to next line and select its message.

M-p
     Move to previous line and select its message.

>
     Move to the last line, and select its message.

<
     Move to the first line, and select its message.

M-s PATTERN RET
     Search through messages for PATTERN starting with the current message; select the message found, and move point in the summary buffer to that message's line.

Deletion, undeletion, and getting new mail, and even selection of a different message all update the summary buffer when you do them in the Rmail buffer.  If the variable rmail-redisplay-summary is non-nil, these actions also bring the summary buffer back onto the screen.

When you are finished using the summary, type w (rmail-summary-wipe) to kill the summary buffer's window.  You can also exit Rmail while in the summary.  q (rmail-summary-quit) kills the summary window, then saves the Rmail file and switches to another buffer.

Editing Within a Message
========================

Rmail mode provides a few special commands for moving within and editing the current message.  In addition, the usual Emacs commands are available (except for a few, such as C-M-n and C-M-h, that are redefined by Rmail for other purposes).  However, the Rmail buffer is normally read-only, and to alter it you must use the Rmail command e described below.

t
     Toggle display of original headers (rmail-toggle-headers).

e
     Edit current message (rmail-edit-current-message).

Rmail reformats the header of each message before displaying it. Normally this involves deleting most header fields, on the grounds that they are not interesting.  The variable rmail-ignored-headers specifies a regexp that matches the header fields to discard in this way.  The original headers are saved permanently, and to see what they look like, use the t command (rmail-toggle-headers).  This discards the reformatted headers of the current message and displays it with the original headers.  Repeating t reformats the message again.  Selecting the message again also reformats.

The Rmail buffer is normally read only, and most of the characters you would type to modify it (including most letters) are redefined as Rmail commands.  This is usually not a problem since it is rare to want to change the text of a message.  When you do want to do this, the way is to type e (rmail-edit-current-message), which changes from Rmail mode into Rmail Edit mode, another major mode which is nearly the same as Text mode. The mode line indicates this change.

In Rmail Edit mode, letters insert themselves as usual and the Rmail commands are not available.  When you are finished editing the message and are ready to go back to Rmail, type C-c C-c, which switches back to Rmail mode.  Alternatively, you can return to Rmail mode but cancel all the editing that you have done by typing C-c C-].

Entering Rmail Edit mode runs the hook text-mode-hook; then it runs the hook rmail-edit-mode-hook (see Hooks).  It adds the attribute edited to the message.

Digest Messages
===============

A digest message is a message which exists to contain and carry several other messages.  Digests are used on some moderated mailing lists; all the messages that arrive for the list during a period of time such as one day are put inside a single digest which is then sent to the subscribers.  Transmitting the single digest uses much less computer time than transmitting the individual messages even though the total size is the same, because the per-message overhead in network mail transmission is considerable.

When you receive a digest message, the most convenient way to read it is to undigestify it: to turn it back into many individual messages. Then you can read and delete the individual messages as it suits you.

To do this, type M-x undigestify-rmail-message after selecting the digest message.  This extracts the submessages as separate Rmail messages, and inserts them following the digest.  The digest message itself is flagged as deleted.

Converting an Rmail File to Mailbox Format
==========================================

The command M-x unrmail converts a file in Rmail format to ordinary system mailbox format, so that you can use it with other mail-editing tools.  You must specify two arguments, the name of the Rmail file and the name to use for the converted file. M-x unrmail does not alter the Rmail file itself.

Reading Rot13 Messages
======================

Mailing list messages that might offend some readers are sometimes encoded in a simple code called rot13---so named because it rotates the alphabet by 13 letters.  This code is not for secrecy, as it provides none; rather, it enables those who might be offended to avoid ever seeing the real text of the message.

To view a buffer using the rot13 code, use the command M-x rot13-other-window.  This displays the current buffer in another window which applies the code when displaying the text.