+@item gnus-picon-news-directories
+@vindex gnus-picon-news-directories
+List of subdirectories to search in @code{gnus-picon-databases} for
+newsgroups faces. @code{("news")} is the default.
+
+@item gnus-picon-user-directories
+@vindex gnus-picon-user-directories
+List of subdirectories to search in @code{gnus-picon-databases} for user
+faces. @code{("users" "usenix" "local" "misc")} is the default.
+
+@item gnus-picon-domain-directories
+@vindex gnus-picon-domain-directories
+List of subdirectories to search in @code{gnus-picon-databases} for
+domain name faces. Defaults to @code{("domains")}. Some people may
+want to add @samp{"unknown"} to this list.
+
+@item gnus-picon-file-types
+@vindex gnus-picon-file-types
+Ordered list of suffixes on picon file names to try. Defaults to
+@code{("xpm" "gif" "xbm")} minus those not builtin your Emacs.
+
+@end table
+
+@node Smileys
+@subsection Smileys
+@cindex smileys
+
+@iftex
+@iflatex
+\gnusfig{-3cm}{0.5cm}{\epsfig{figure=ps/BigFace,height=20cm}}
+\input{smiley}
+@end iflatex
+@end iftex
+
+@dfn{Smiley} is a package separate from Gnus, but since Gnus is
+currently the only package that uses Smiley, it is documented here.
+
+In short---to use Smiley in Gnus, put the following in your
+@file{~/.gnus.el} file:
+
+@lisp
+(setq gnus-treat-display-smileys t)
+@end lisp
+
+Smiley maps text smiley faces---@samp{:-)}, @samp{8-)}, @samp{:-(} and
+the like---to pictures and displays those instead of the text smiley
+faces. The conversion is controlled by a list of regexps that matches
+text and maps that to file names.
+
+@vindex smiley-regexp-alist
+The alist used is specified by the @code{smiley-regexp-alist}
+variable. The first item in each element is the regexp to be matched;
+the second element is the regexp match group that is to be replaced by
+the picture; and the third element is the name of the file to be
+displayed.
+
+The following variables customize where Smiley will look for these
+files:
+
+@table @code
+
+@item smiley-data-directory
+@vindex smiley-data-directory
+Where Smiley will look for smiley faces files.
+
+@item gnus-smiley-file-types
+@vindex gnus-smiley-file-types
+List of suffixes on smiley file names to try.
+
+@end table
+
+
+@node X-Face
+@subsection X-Face
+@cindex x-face
+
+@code{X-Face} headers describe a 48x48 pixel black-and-white (1 bit
+depth) image that's supposed to represent the author of the message.
+It seems to be supported by an ever-growing number of mail and news
+readers.
+
+@cindex x-face
+@findex gnus-article-display-x-face
+@findex gnus-article-x-face-command
+@vindex gnus-article-x-face-command
+@vindex gnus-article-x-face-too-ugly
+@iftex
+@iflatex
+\include{xface}
+@end iflatex
+@end iftex
+@c @anchor{X-Face}
+
+Decoding an @code{X-Face} header either requires an Emacs that has
+@samp{compface} support (which most XEmacs versions has), or that you
+have @samp{compface} installed on your system. If either is true,
+Gnus will default to displaying @code{X-Face} headers.
+
+The variable that controls this is the
+@code{gnus-article-x-face-command} variable. If this variable is a
+string, this string will be executed in a sub-shell. If it is a
+function, this function will be called with the face as the argument.
+If the @code{gnus-article-x-face-too-ugly} (which is a regexp) matches
+the @code{From} header, the face will not be shown.
+
+The default action under Emacs 20 is to fork off the @code{display}
+program@footnote{@code{display} is from the ImageMagick package. For
+the @code{uncompface} and @code{icontopbm} programs look for a package
+like @code{compface} or @code{faces-xface} on a GNU/Linux system.} to
+view the face.
+
+Under XEmacs or Emacs 21+ with suitable image support, the default
+action is to display the face before the @code{From} header. (It's
+nicer if XEmacs has been compiled with @code{X-Face} support---that
+will make display somewhat faster. If there's no native @code{X-Face}
+support, Gnus will try to convert the @code{X-Face} header using
+external programs from the @code{pbmplus} package and
+friends.@footnote{On a GNU/Linux system look for packages with names
+like @code{netpbm}, @code{libgr-progs} and @code{compface}.})
+
+(Note: @code{x-face} is used in the variable/function names, not
+@code{xface}).
+
+Gnus provides a few convenience functions and variables to allow
+easier insertion of X-Face headers in outgoing messages.
+
+@findex gnus-random-x-face
+@vindex gnus-convert-pbm-to-x-face-command
+@vindex gnus-x-face-directory
+@code{gnus-random-x-face} goes through all the @samp{pbm} files in
+@code{gnus-x-face-directory} and picks one at random, and then
+converts it to the X-Face format by using the
+@code{gnus-convert-pbm-to-x-face-command} shell command. The
+@samp{pbm} files should be 48x48 pixels big. It returns the X-Face
+header data as a string.
+
+@findex gnus-insert-random-x-face-header
+@code{gnus-insert-random-x-face-header} calls
+@code{gnus-random-x-face} and inserts a @samp{X-Face} header with the
+randomly generated data.
+
+@findex gnus-x-face-from-file
+@vindex gnus-convert-image-to-x-face-command
+@code{gnus-x-face-from-file} takes a GIF file as the parameter, and then
+converts the file to X-Face format by using the
+@code{gnus-convert-image-to-x-face-command} shell command.
+
+Here's how you would typically use the first function. Put something
+like the following in your @file{~/.gnus.el} file:
+
+@lisp
+(setq message-required-news-headers
+ (nconc message-required-news-headers
+ (list '(X-Face . gnus-random-x-face))))
+@end lisp
+
+Using the last function would be something like this:
+
+@lisp
+(setq message-required-news-headers
+ (nconc message-required-news-headers
+ (list '(X-Face . (lambda ()
+ (gnus-x-face-from-file
+ "~/My-face.gif"))))))
+@end lisp
+
+
+@node XVarious
+@subsection Various XEmacs Variables
+
+@table @code
+@item gnus-xmas-glyph-directory
+@vindex gnus-xmas-glyph-directory
+This is where Gnus will look for pictures. Gnus will normally
+auto-detect this directory, but you may set it manually if you have an
+unusual directory structure.
+
+@item gnus-xmas-logo-color-alist
+@vindex gnus-xmas-logo-color-alist
+This is an alist where the key is a type symbol and the values are the
+foreground and background color of the splash page glyph.
+
+@item gnus-xmas-logo-color-style
+@vindex gnus-xmas-logo-color-style
+This is the key used to look up the color in the alist described above.
+Valid values include @code{flame}, @code{pine}, @code{moss},
+@code{irish}, @code{sky}, @code{tin}, @code{velvet}, @code{grape},
+@code{labia}, @code{berry}, @code{neutral}, and @code{september}.
+
+@item gnus-xmas-modeline-glyph
+@vindex gnus-xmas-modeline-glyph
+A glyph displayed in all Gnus mode lines. It is a tiny gnu head by
+default.
+
+@end table
+
+@subsubsection Toolbar
+
+@table @code
+
+@item gnus-use-toolbar
+@vindex gnus-use-toolbar
+If @code{nil}, don't display toolbars. If non-@code{nil}, it should be
+one of @code{default-toolbar}, @code{top-toolbar}, @code{bottom-toolbar},
+@code{right-toolbar}, or @code{left-toolbar}.
+
+@item gnus-group-toolbar
+@vindex gnus-group-toolbar
+The toolbar in the group buffer.
+
+@item gnus-summary-toolbar
+@vindex gnus-summary-toolbar
+The toolbar in the summary buffer.
+
+@item gnus-summary-mail-toolbar
+@vindex gnus-summary-mail-toolbar
+The toolbar in the summary buffer of mail groups.
+
+@end table
+
+@iftex
+@iflatex
+\margindex{}
+@end iflatex
+@end iftex
+
+
+@node Fuzzy Matching
+@section Fuzzy Matching
+@cindex fuzzy matching
+
+Gnus provides @dfn{fuzzy matching} of @code{Subject} lines when doing
+things like scoring, thread gathering and thread comparison.
+
+As opposed to regular expression matching, fuzzy matching is very fuzzy.
+It's so fuzzy that there's not even a definition of what @dfn{fuzziness}
+means, and the implementation has changed over time.
+
+Basically, it tries to remove all noise from lines before comparing.
+@samp{Re: }, parenthetical remarks, white space, and so on, are filtered
+out of the strings before comparing the results. This often leads to
+adequate results---even when faced with strings generated by text
+manglers masquerading as newsreaders.
+
+
+@node Thwarting Email Spam
+@section Thwarting Email Spam
+@cindex email spam
+@cindex spam
+@cindex UCE
+@cindex unsolicited commercial email
+
+In these last days of the Usenet, commercial vultures are hanging about
+and grepping through news like crazy to find email addresses they can
+foist off their scams and products to. As a reaction to this, many
+people have started putting nonsense addresses into their @code{From}
+lines. I think this is counterproductive---it makes it difficult for
+people to send you legitimate mail in response to things you write, as
+well as making it difficult to see who wrote what. This rewriting may
+perhaps be a bigger menace than the unsolicited commercial email itself
+in the end.
+
+The biggest problem I have with email spam is that it comes in under
+false pretenses. I press @kbd{g} and Gnus merrily informs me that I
+have 10 new emails. I say ``Golly gee! Happy is me!'' and select the
+mail group, only to find two pyramid schemes, seven advertisements
+(``New! Miracle tonic for growing full, lustrous hair on your toes!'')
+and one mail asking me to repent and find some god.
+
+This is annoying. Here's what you can do about it.
+
+@menu
+* The problem of spam:: Some background, and some solutions
+* Anti-Spam Basics:: Simple steps to reduce the amount of spam.
+* SpamAssassin:: How to use external anti-spam tools.
+* Hashcash:: Reduce spam by burning CPU time.
+* Filtering Spam Using The Spam ELisp Package::
+* Filtering Spam Using Statistics with spam-stat::
+@end menu
+
+@node The problem of spam
+@subsection The problem of spam
+@cindex email spam
+@cindex spam filtering approaches
+@cindex filtering approaches, spam
+@cindex UCE
+@cindex unsolicited commercial email
+
+First, some background on spam.
+
+If you have access to e-mail, you are familiar with spam (technically
+termed @acronym{UCE}, Unsolicited Commercial E-mail). Simply put, it exists
+because e-mail delivery is very cheap compared to paper mail, so only
+a very small percentage of people need to respond to an UCE to make it
+worthwhile to the advertiser. Ironically, one of the most common
+spams is the one offering a database of e-mail addresses for further
+spamming. Senders of spam are usually called @emph{spammers}, but terms like
+@emph{vermin}, @emph{scum}, and @emph{morons} are in common use as well.
+
+Spam comes from a wide variety of sources. It is simply impossible to
+dispose of all spam without discarding useful messages. A good
+example is the TMDA system, which requires senders
+unknown to you to confirm themselves as legitimate senders before
+their e-mail can reach you. Without getting into the technical side
+of TMDA, a downside is clearly that e-mail from legitimate sources may
+be discarded if those sources can't or won't confirm themselves
+through the TMDA system. Another problem with TMDA is that it
+requires its users to have a basic understanding of e-mail delivery
+and processing.
+
+The simplest approach to filtering spam is filtering. If you get 200
+spam messages per day from @samp{random-address@@vmadmin.com}, you
+block @samp{vmadmin.com}. If you get 200 messages about
+@samp{VIAGRA}, you discard all messages with @samp{VIAGRA} in the
+message. This, unfortunately, is a great way to discard legitimate
+e-mail. For instance, the very informative and useful RISKS digest
+has been blocked by overzealous mail filters because it
+@strong{contained} words that were common in spam messages.
+Nevertheless, in isolated cases, with great care, direct filtering of
+mail can be useful.
+
+Another approach to filtering e-mail is the distributed spam
+processing, for instance DCC implements such a system. In essence,
+@code{N} systems around the world agree that a machine @samp{X} in
+China, Ghana, or California is sending out spam e-mail, and these
+@code{N} systems enter @samp{X} or the spam e-mail from @samp{X} into
+a database. The criteria for spam detection vary---it may be the
+number of messages sent, the content of the messages, and so on. When
+a user of the distributed processing system wants to find out if a
+message is spam, he consults one of those @code{N} systems.
+
+Distributed spam processing works very well against spammers that send
+a large number of messages at once, but it requires the user to set up
+fairly complicated checks. There are commercial and free distributed
+spam processing systems. Distributed spam processing has its risks as
+well. For instance legitimate e-mail senders have been accused of
+sending spam, and their web sites have been shut down for some time
+because of the incident.
+
+The statistical approach to spam filtering is also popular. It is
+based on a statistical analysis of previous spam messages. Usually
+the analysis is a simple word frequency count, with perhaps pairs of
+words or 3-word combinations thrown into the mix. Statistical
+analysis of spam works very well in most of the cases, but it can
+classify legitimate e-mail as spam in some cases. It takes time to
+run the analysis, the full message must be analyzed, and the user has
+to store the database of spam analyses.
+
+@node Anti-Spam Basics
+@subsection Anti-Spam Basics
+@cindex email spam
+@cindex spam
+@cindex UCE
+@cindex unsolicited commercial email
+
+One way of dealing with spam is having Gnus split out all spam into a
+@samp{spam} mail group (@pxref{Splitting Mail}).
+
+First, pick one (1) valid mail address that you can be reached at, and
+put it in your @code{From} header of all your news articles. (I've
+chosen @samp{larsi@@trym.ifi.uio.no}, but for many addresses on the form
+@samp{larsi+usenet@@ifi.uio.no} will be a better choice. Ask your
+sysadmin whether your sendmail installation accepts keywords in the local
+part of the mail address.)
+
+@lisp
+(setq message-default-news-headers
+ "From: Lars Magne Ingebrigtsen <larsi@@trym.ifi.uio.no>\n")
+@end lisp
+
+Then put the following split rule in @code{nnmail-split-fancy}
+(@pxref{Fancy Mail Splitting}):
+
+@lisp
+(
+ ...
+ (to "larsi@@trym.ifi.uio.no"
+ (| ("subject" "re:.*" "misc")
+ ("references" ".*@@.*" "misc")
+ "spam"))
+ ...
+)
+@end lisp
+
+This says that all mail to this address is suspect, but if it has a
+@code{Subject} that starts with a @samp{Re:} or has a @code{References}
+header, it's probably ok. All the rest goes to the @samp{spam} group.
+(This idea probably comes from Tim Pierce.)
+
+In addition, many mail spammers talk directly to your @acronym{SMTP} server
+and do not include your email address explicitly in the @code{To}
+header. Why they do this is unknown---perhaps it's to thwart this
+thwarting scheme? In any case, this is trivial to deal with---you just
+put anything not addressed to you in the @samp{spam} group by ending
+your fancy split rule in this way:
+
+@lisp
+(
+ ...
+ (to "larsi" "misc")
+ "spam")
+@end lisp
+
+In my experience, this will sort virtually everything into the right
+group. You still have to check the @samp{spam} group from time to time to
+check for legitimate mail, though. If you feel like being a good net
+citizen, you can even send off complaints to the proper authorities on
+each unsolicited commercial email---at your leisure.
+
+If you are also a lazy net citizen, you will probably prefer complaining
+automatically with the @file{gnus-junk.el} package, available FOR FREE
+at @* @uref{http://stud2.tuwien.ac.at/~e9426626/gnus-junk.html}.
+Since most e-mail spam is sent automatically, this may reconcile the
+cosmic balance somewhat.
+
+This works for me. It allows people an easy way to contact me (they can
+just press @kbd{r} in the usual way), and I'm not bothered at all with
+spam. It's a win-win situation. Forging @code{From} headers to point
+to non-existent domains is yucky, in my opinion.
+
+
+
+@node SpamAssassin
+@subsection SpamAssassin, Vipul's Razor, DCC, etc
+@cindex SpamAssassin
+@cindex Vipul's Razor
+@cindex DCC
+
+The days where the hints in the previous section was sufficient in
+avoiding spam is coming to an end. There are many tools out there
+that claim to reduce the amount of spam you get. This section could
+easily become outdated fast, as new products replace old, but
+fortunately most of these tools seem to have similar interfaces. Even
+though this section will use SpamAssassin as an example, it should be
+easy to adapt it to most other tools.
+
+If the tool you are using is not installed on the mail server, you
+need to invoke it yourself. Ideas on how to use the
+@code{:postscript} mail source parameter (@pxref{Mail Source
+Specifiers}) follows.
+
+@lisp
+(setq mail-sources
+ '((file :prescript "formail -bs spamassassin < /var/mail/%u")
+ (pop :user "jrl"
+ :server "pophost"
+ :postscript "mv %t /tmp/foo; formail -bs spamc < /tmp/foo > %t")))
+@end lisp
+
+Once you managed to process your incoming spool somehow, thus making
+the mail contain e.g. a header indicating it is spam, you are ready to
+filter it out. Using normal split methods (@pxref{Splitting Mail}):
+
+@lisp
+(setq nnmail-split-methods '(("spam" "^X-Spam-Flag: YES")
+ ...))
+@end lisp
+
+Or using fancy split methods (@pxref{Fancy Mail Splitting}):
+
+@lisp
+(setq nnmail-split-methods 'nnmail-split-fancy
+ nnmail-split-fancy '(| ("X-Spam-Flag" "YES" "spam")
+ ...))
+@end lisp
+
+Some people might not like the idea of piping the mail through various
+programs using a @code{:prescript} (if some program is buggy, you
+might lose all mail). If you are one of them, another solution is to
+call the external tools during splitting. Example fancy split method:
+
+@lisp
+(setq nnmail-split-fancy '(| (: kevin-spamassassin)
+ ...))
+(defun kevin-spamassassin ()
+ (save-excursion
+ (let ((buf (or (get-buffer " *nnmail incoming*")
+ (get-buffer " *nnml move*"))))
+ (if (not buf)
+ (progn (message "Oops, cannot find message buffer") nil)
+ (set-buffer buf)
+ (if (eq 1 (call-process-region (point-min) (point-max)
+ "spamc" nil nil nil "-c"))
+ "spam")))))
+@end lisp
+
+That is about it. As some spam is likely to get through anyway, you
+might want to have a nifty function to call when you happen to read
+spam. And here is the nifty function:
+
+@lisp
+ (defun my-gnus-raze-spam ()
+ "Submit SPAM to Vipul's Razor, then mark it as expirable."
+ (interactive)
+ (gnus-summary-show-raw-article)
+ (gnus-summary-save-in-pipe "razor-report -f -d")
+ (gnus-summary-mark-as-expirable 1))
+@end lisp
+
+@node Hashcash
+@subsection Hashcash
+@cindex hashcash
+
+A novel technique to fight spam is to require senders to do something
+costly for each message they send. This has the obvious drawback that
+you cannot rely on that everyone in the world uses this technique,
+since it is not part of the Internet standards, but it may be useful
+in smaller communities.
+
+While the tools in the previous section work well in practice, they
+work only because the tools are constantly maintained and updated as
+new form of spam appears. This means that a small percentage of spam
+will always get through. It also means that somewhere, someone needs
+to read lots of spam to update these tools. Hashcash avoids that, but
+instead requires that everyone you communicate with supports the
+scheme. You can view the two approaches as pragmatic vs dogmatic.
+The approaches have their own advantages and disadvantages, but as
+often in the real world, a combination of them is stronger than either
+one of them separately.
+
+@cindex X-Hashcash
+The ``something costly'' is to burn CPU time, more specifically to
+compute a hash collision up to a certain number of bits. The
+resulting hashcash cookie is inserted in a @samp{X-Hashcash:}
+header. For more details, and for the external application
+@code{hashcash} you need to install to use this feature, see
+@uref{http://www.cypherspace.org/~adam/hashcash/}. Even more
+information can be found at @uref{http://www.camram.org/}.
+
+If you wish to call hashcash for each message you send, say something
+like:
+
+@lisp
+(require 'hashcash)
+(add-hook 'message-send-hook 'mail-add-payment)
+@end lisp
+
+The @code{hashcash.el} library can be found at
+@uref{http://users.actrix.gen.nz/mycroft/hashcash.el}, or in the Gnus
+development contrib directory.
+
+You will need to set up some additional variables as well:
+
+@table @code
+
+@item hashcash-default-payment
+@vindex hashcash-default-payment
+This variable indicates the default number of bits the hash collision
+should consist of. By default this is 0, meaning nothing will be
+done. Suggested useful values include 17 to 29.
+
+@item hashcash-payment-alist
+@vindex hashcash-payment-alist
+Some receivers may require you to spend burn more CPU time than the
+default. This variable contains a list of @samp{(@var{addr}
+@var{amount})} cells, where @var{addr} is the receiver (email address
+or newsgroup) and @var{amount} is the number of bits in the collision
+that is needed. It can also contain @samp{(@var{addr} @var{string}
+@var{amount})} cells, where the @var{string} is the string to use
+(normally the email address or newsgroup name is used).
+
+@item hashcash
+@vindex hashcash
+Where the @code{hashcash} binary is installed.
+
+@end table
+
+Currently there is no built in functionality in Gnus to verify
+hashcash cookies, it is expected that this is performed by your hand
+customized mail filtering scripts. Improvements in this area would be
+a useful contribution, however.
+
+@node Filtering Spam Using The Spam ELisp Package
+@subsection Filtering Spam Using The Spam ELisp Package
+@cindex spam filtering
+@cindex spam
+
+The idea behind @code{spam.el} is to have a control center for spam detection
+and filtering in Gnus. To that end, @code{spam.el} does two things: it
+filters incoming mail, and it analyzes mail known to be spam or ham.
+@emph{Ham} is the name used throughout @code{spam.el} to indicate
+non-spam messages.
+
+So, what happens when you load @code{spam.el}? First of all, you get
+the following keyboard commands:
+
+@table @kbd
+
+@item M-d
+@itemx M s x
+@itemx S x
+@kindex M-d
+@kindex S x
+@kindex M s x
+@findex gnus-summary-mark-as-spam
+@code{gnus-summary-mark-as-spam}.
+
+Mark current article as spam, showing it with the @samp{$} mark.
+Whenever you see a spam article, make sure to mark its summary line
+with @kbd{M-d} before leaving the group. This is done automatically
+for unread articles in @emph{spam} groups.
+
+@item M s t
+@itemx S t
+@kindex M s t
+@kindex S t
+@findex spam-bogofilter-score
+@code{spam-bogofilter-score}.
+
+You must have Bogofilter installed for that command to work properly.
+
+@xref{Bogofilter}.
+
+@end table
+
+Also, when you load @code{spam.el}, you will be able to customize its
+variables. Try @code{customize-group} on the @samp{spam} variable
+group.
+
+The concepts of ham processors and spam processors are very important.
+Ham processors and spam processors for a group can be set with the
+@code{spam-process} group parameter, or the
+@code{gnus-spam-process-newsgroups} variable. Ham processors take
+mail known to be non-spam (@emph{ham}) and process it in some way so
+that later similar mail will also be considered non-spam. Spam
+processors take mail known to be spam and process it so similar spam
+will be detected later.
+
+Gnus learns from the spam you get. You have to collect your spam in
+one or more spam groups, and set or customize the variable
+@code{spam-junk-mailgroups} as appropriate. You can also declare
+groups to contain spam by setting their group parameter
+@code{spam-contents} to @code{gnus-group-spam-classification-spam}, or
+by customizing the corresponding variable
+@code{gnus-spam-newsgroup-contents}. The @code{spam-contents} group
+parameter and the @code{gnus-spam-newsgroup-contents} variable can
+also be used to declare groups as @emph{ham} groups if you set their
+classification to @code{gnus-group-spam-classification-ham}. If
+groups are not classified by means of @code{spam-junk-mailgroups},
+@code{spam-contents}, or @code{gnus-spam-newsgroup-contents}, they are
+considered @emph{unclassified}. All groups are unclassified by
+default.
+
+In spam groups, all messages are considered to be spam by default:
+they get the @samp{$} mark when you enter the group. You must review
+these messages from time to time and remove the @samp{$} mark for
+every message that is not spam after all. To remove the @samp{$}
+mark, you can use @kbd{M-u} to ``unread'' the article, or @kbd{d} for
+declaring it read the non-spam way. When you leave a group, all
+spam-marked (@samp{$}) articles are sent to a spam processor which
+will study them as spam samples.
+
+Messages may also be deleted in various other ways, and unless
+@code{spam-ham-marks} gets overridden below, marks @samp{R} and
+@samp{r} for default read or explicit delete, marks @samp{X} and
+@samp{K} for automatic or explicit kills, as well as mark @samp{Y} for
+low scores, are all considered to be associated with articles which
+are not spam. This assumption might be false, in particular if you
+use kill files or score files as means for detecting genuine spam, you
+should then adjust the @code{spam-ham-marks} variable.
+
+@defvar spam-ham-marks
+You can customize this variable to be the list of marks you want to
+consider ham. By default, the list contains the deleted, read,
+killed, kill-filed, and low-score marks.
+@end defvar
+
+@defvar spam-spam-marks
+You can customize this variable to be the list of marks you want to
+consider spam. By default, the list contains only the spam mark.
+@end defvar
+
+When you leave @emph{any} group, regardless of its
+@code{spam-contents} classification, all spam-marked articles are sent
+to a spam processor, which will study these as spam samples. If you
+explicit kill a lot, you might sometimes end up with articles marked
+@samp{K} which you never saw, and which might accidentally contain
+spam. Best is to make sure that real spam is marked with @samp{$},
+and nothing else.
+
+When you leave a @emph{spam} group, all spam-marked articles are
+marked as expired after processing with the spam processor. This is
+not done for @emph{unclassified} or @emph{ham} groups. Also, any
+@strong{ham} articles in a spam group will be moved to a location
+determined by either the @code{ham-process-destination} group
+parameter or a match in the @code{gnus-ham-process-destinations}
+variable, which is a list of regular expressions matched with group
+names (it's easiest to customize this variable with
+@code{customize-variable gnus-ham-process-destinations}). The ultimate
+location is a group name. If the @code{ham-process-destination}
+parameter is not set, spam articles are only expired.
+
+When you leave a @emph{ham} group, all ham-marked articles are sent to
+a ham processor, which will study these as non-spam samples.
+
+When you leave a @emph{ham} or @emph{unclassified} group, all
+@strong{spam} articles are moved to a location determined by either
+the @code{spam-process-destination} group parameter or a match in the
+@code{gnus-spam-process-destinations} variable, which is a list of
+regular expressions matched with group names (it's easiest to
+customize this variable with @code{customize-variable
+gnus-spam-process-destinations}). The ultimate location is a group
+name. If the @code{spam-process-destination} parameter is not set,
+the spam articles are only expired.
+
+To use the @code{spam.el} facilities for incoming mail filtering, you
+must add the following to your fancy split list
+@code{nnmail-split-fancy} or @code{nnimap-split-fancy}:
+
+@example
+(: spam-split)
+@end example
+
+Note that the fancy split may be called @code{nnmail-split-fancy} or
+@code{nnimap-split-fancy}, depending on whether you use the nnmail or
+nnimap back ends to retrieve your mail.
+
+The @code{spam-split} function will process incoming mail and send the
+mail considered to be spam into the group name given by the variable
+@code{spam-split-group}. By default that group name is @samp{spam},
+but you can customize it.
+
+@emph{Note for IMAP users}
+
+The boolean variable @code{nnimap-split-download-body} needs to be
+set, if you want to split based on the whole message instead of just
+the headers. By default, the nnimap backend will only retrieve the
+message headers. If you use @code{spam-check-bogofilter},
+@code{spam-check-ifile}, or @code{spam-check-stat} (the splitters that
+can benefit from the full message body), you should set this variable.
+It is not set by default because it will slow @acronym{IMAP} down.
+
+@xref{Splitting in IMAP}.
+
+@emph{TODO: Currently, spam.el only supports insertion of articles
+into a backend. There is no way to tell spam.el that an article is no
+longer spam or ham.}
+
+@emph{TODO: spam.el needs to provide a uniform way of training all the
+statistical databases. Some have that functionality built-in, others
+don't.}
+
+The following are the methods you can use to control the behavior of
+@code{spam-split} and their corresponding spam and ham processors:
+
+@menu
+* Blacklists and Whitelists::
+* BBDB Whitelists::
+* Blackholes::
+* Regular Expressions Header Matching::
+* Bogofilter::
+* ifile spam filtering::
+* spam-stat spam filtering::
+* Extending the spam elisp package::
+@end menu
+
+@node Blacklists and Whitelists
+@subsubsection Blacklists and Whitelists
+@cindex spam filtering
+@cindex whitelists, spam filtering
+@cindex blacklists, spam filtering
+@cindex spam
+
+@defvar spam-use-blacklist
+
+Set this variable to @code{t} if you want to use blacklists when
+splitting incoming mail. Messages whose senders are in the blacklist
+will be sent to the @code{spam-split-group}. This is an explicit
+filter, meaning that it acts only on mail senders @emph{declared} to
+be spammers.
+
+@end defvar
+
+@defvar spam-use-whitelist
+
+Set this variable to @code{t} if you want to use whitelists when
+splitting incoming mail. Messages whose senders are not in the
+whitelist will be sent to the next spam-split rule. This is an
+explicit filter, meaning that unless someone is in the whitelist, their
+messages are not assumed to be spam or ham.
+
+@end defvar
+
+@defvar spam-use-whitelist-exclusive
+
+Set this variable to @code{t} if you want to use whitelists as an
+implicit filter, meaning that every message will be considered spam
+unless the sender is in the whitelist. Use with care.
+
+@end defvar
+
+@defvar gnus-group-spam-exit-processor-blacklist
+
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the senders of
+spam-marked articles will be added to the blacklist.
+
+@end defvar
+
+@defvar gnus-group-ham-exit-processor-whitelist
+
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the senders of
+ham-marked articles in @emph{ham} groups will be added to the
+whitelist. Note that this ham processor has no effect in @emph{spam}
+or @emph{unclassified} groups.
+
+@end defvar
+
+Blacklists are lists of regular expressions matching addresses you
+consider to be spam senders. For instance, to block mail from any
+sender at @samp{vmadmin.com}, you can put @samp{vmadmin.com} in your
+blacklist. You start out with an empty blacklist. Blacklist entries
+use the Emacs regular expression syntax.
+
+Conversely, whitelists tell Gnus what addresses are considered
+legitimate. All messages from whitelisted addresses are considered
+non-spam. Also see @ref{BBDB Whitelists}. Whitelist entries use the
+Emacs regular expression syntax.
+
+The blacklist and whitelist file locations can be customized with the
+@code{spam-directory} variable (@file{~/News/spam} by default), or
+the @code{spam-whitelist} and @code{spam-blacklist} variables
+directly. The whitelist and blacklist files will by default be in the
+@code{spam-directory} directory, named @file{whitelist} and
+@file{blacklist} respectively.
+
+@node BBDB Whitelists
+@subsubsection BBDB Whitelists
+@cindex spam filtering
+@cindex BBDB whitelists, spam filtering
+@cindex BBDB, spam filtering
+@cindex spam
+
+@defvar spam-use-BBDB
+
+Analogous to @code{spam-use-whitelist} (@pxref{Blacklists and
+Whitelists}), but uses the BBDB as the source of whitelisted
+addresses, without regular expressions. You must have the BBDB loaded
+for @code{spam-use-BBDB} to work properly. Messages whose senders are
+not in the BBDB will be sent to the next spam-split rule. This is an
+explicit filter, meaning that unless someone is in the BBDB, their
+messages are not assumed to be spam or ham.
+
+@end defvar
+
+@defvar spam-use-BBDB-exclusive
+
+Set this variable to @code{t} if you want to use the BBDB as an
+implicit filter, meaning that every message will be considered spam
+unless the sender is in the BBDB. Use with care. Only sender
+addresses in the BBDB will be allowed through; all others will be
+classified as spammers.
+
+@end defvar
+
+@defvar gnus-group-ham-exit-processor-BBDB
+
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the senders of
+ham-marked articles in @emph{ham} groups will be added to the
+BBDB. Note that this ham processor has no effect in @emph{spam}
+or @emph{unclassified} groups.
+
+@end defvar
+
+@node Blackholes
+@subsubsection Blackholes
+@cindex spam filtering
+@cindex blackholes, spam filtering
+@cindex spam
+
+@defvar spam-use-blackholes
+
+This option is disabled by default. You can let Gnus consult the
+blackhole-type distributed spam processing systems (DCC, for instance)
+when you set this option. The variable @code{spam-blackhole-servers}
+holds the list of blackhole servers Gnus will consult. The current
+list is fairly comprehensive, but make sure to let us know if it
+contains outdated servers.
+
+The blackhole check uses the @code{dig.el} package, but you can tell
+@code{spam.el} to use @code{dns.el} instead for better performance if
+you set @code{spam-use-dig} to @code{nil}. It is not recommended at
+this time to set @code{spam-use-dig} to @code{nil} despite the
+possible performance improvements, because some users may be unable to
+use it, but you can try it and see if it works for you.
+
+@end defvar
+
+@defvar spam-blackhole-servers
+
+The list of servers to consult for blackhole checks.
+
+@end defvar
+
+@defvar spam-blackhole-good-server-regex
+
+A regular expression for IPs that should not be checked against the
+blackhole server list. When set to @code{nil}, it has no effect.
+
+@end defvar
+
+@defvar spam-use-dig
+
+Use the @code{dig.el} package instead of the @code{dns.el} package.
+The default setting of @code{t} is recommended.
+
+@end defvar
+
+Blackhole checks are done only on incoming mail. There is no spam or
+ham processor for blackholes.
+
+@node Regular Expressions Header Matching
+@subsubsection Regular Expressions Header Matching
+@cindex spam filtering
+@cindex regular expressions header matching, spam filtering
+@cindex spam
+
+@defvar spam-use-regex-headers
+
+This option is disabled by default. You can let Gnus check the
+message headers against lists of regular expressions when you set this
+option. The variables @code{spam-regex-headers-spam} and
+@code{spam-regex-headers-ham} hold the list of regular expressions.
+Gnus will check against the message headers to determine if the
+message is spam or ham, respectively.
+
+@end defvar
+
+@defvar spam-regex-headers-spam
+
+The list of regular expressions that, when matched in the headers of
+the message, positively identify it as spam.
+
+@end defvar
+
+@defvar spam-regex-headers-ham
+
+The list of regular expressions that, when matched in the headers of
+the message, positively identify it as ham.
+
+@end defvar
+
+Regular expression header checks are done only on incoming mail.
+There is no specific spam or ham processor for regular expressions.
+
+@node Bogofilter
+@subsubsection Bogofilter
+@cindex spam filtering
+@cindex bogofilter, spam filtering
+@cindex spam
+
+@defvar spam-use-bogofilter
+
+Set this variable if you want @code{spam-split} to use Eric Raymond's
+speedy Bogofilter.
+
+With a minimum of care for associating the @samp{$} mark for spam
+articles only, Bogofilter training all gets fairly automatic. You
+should do this until you get a few hundreds of articles in each
+category, spam or not. The command @kbd{S t} in summary mode, either
+for debugging or for curiosity, shows the @emph{spamicity} score of
+the current article (between 0.0 and 1.0).
+
+Bogofilter determines if a message is spam based on an internal
+threshold, set at compilation time. That threshold can't be
+customized.
+
+If the @code{bogofilter} executable is not in your path, Bogofilter
+processing will be turned off.
+
+You should not enable this if you use @code{spam-use-bogofilter-headers}.
+
+@end defvar
+
+@defvar spam-use-bogofilter-headers
+
+Set this variable if you want @code{spam-split} to use Eric Raymond's
+speedy Bogofilter, looking only at the message headers. It works
+similarly to @code{spam-use-bogofilter}, but the @code{X-Bogosity} header
+must be in the message already. Normally you would do this with a
+procmail recipe or something similar; consult the Bogofilter
+installation documents for details.
+
+You should not enable this if you use @code{spam-use-bogofilter}.
+
+@end defvar
+
+@defvar gnus-group-spam-exit-processor-bogofilter
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, spam-marked articles
+will be added to the Bogofilter spam database.
+@end defvar
+
+@defvar gnus-group-ham-exit-processor-bogofilter
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the ham-marked
+articles in @emph{ham} groups will be added to the Bogofilter database
+of non-spam messages. Note that this ham processor has no effect in
+@emph{spam} or @emph{unclassified} groups.
+@end defvar
+
+@defvar spam-bogofilter-database-directory
+
+This is the directory where Bogofilter will store its databases. It
+is not specified by default, so Bogofilter will use its own default
+database directory.
+
+@end defvar
+
+The Bogofilter mail classifier is similar to ifile in intent and
+purpose. A ham and a spam processor are provided, plus the
+@code{spam-use-bogofilter} and @code{spam-use-bogofilter-headers}
+variables to indicate to spam-split that Bogofilter should either be
+used, or has already been used on the article. The 0.9.2.1 version of
+Bogofilter was used to test this functionality.
+
+@node ifile spam filtering
+@subsubsection ifile spam filtering
+@cindex spam filtering
+@cindex ifile, spam filtering
+@cindex spam
+
+@defvar spam-use-ifile
+
+Enable this variable if you want @code{spam-split} to use ifile, a
+statistical analyzer similar to Bogofilter.
+
+@end defvar
+
+@defvar spam-ifile-all-categories
+
+Enable this variable if you want @code{spam-use-ifile} to give you all
+the ifile categories, not just spam/non-spam. If you use this, make
+sure you train ifile as described in its documentation.
+
+@end defvar
+
+@defvar spam-ifile-spam-category
+
+This is the category of spam messages as far as ifile is concerned.
+The actual string used is irrelevant, but you probably want to leave
+the default value of @samp{spam}.
+@end defvar
+
+@defvar spam-ifile-database-path
+
+This is the filename for the ifile database. It is not specified by
+default, so ifile will use its own default database name.
+
+@end defvar
+
+The ifile mail classifier is similar to Bogofilter in intent and
+purpose. A ham and a spam processor are provided, plus the
+@code{spam-use-ifile} variable to indicate to spam-split that ifile
+should be used. The 1.2.1 version of ifile was used to test this
+functionality.
+
+@node spam-stat spam filtering
+@subsubsection spam-stat spam filtering
+@cindex spam filtering
+@cindex spam-stat, spam filtering
+@cindex spam-stat
+@cindex spam
+
+@xref{Filtering Spam Using Statistics with spam-stat}.
+
+@defvar spam-use-stat
+
+Enable this variable if you want @code{spam-split} to use
+spam-stat.el, an Emacs Lisp statistical analyzer.
+
+@end defvar
+
+@defvar gnus-group-spam-exit-processor-stat
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the spam-marked
+articles will be added to the spam-stat database of spam messages.
+@end defvar
+
+@defvar gnus-group-ham-exit-processor-stat
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameters or the
+@code{gnus-spam-process-newsgroups} variable. When this symbol is
+added to a group's @code{spam-process} parameter, the ham-marked
+articles in @emph{ham} groups will be added to the spam-stat database
+of non-spam messages. Note that this ham processor has no effect in
+@emph{spam} or @emph{unclassified} groups.
+@end defvar
+
+This enables spam.el to cooperate with spam-stat.el. spam-stat.el
+provides an internal (Lisp-only) spam database, which unlike ifile or
+Bogofilter does not require external programs. A spam and a ham
+processor, and the @code{spam-use-stat} variable for @code{spam-split}
+are provided.
+
+@node Extending the spam elisp package
+@subsubsection Extending the spam elisp package
+@cindex spam filtering
+@cindex spam elisp package, extending
+@cindex extending the spam elisp package
+
+Say you want to add a new back end called blackbox. For filtering
+incoming mail, provide the following:
+
+@enumerate