+@lisp
+("clewis@@ferret.ocunix.on.ca" (not ".*") "spew" "spam")
+@end lisp
+
+The specs are applied left-to-right.
+
+
+@item gnus-nocem-verifyer
+@vindex gnus-nocem-verifyer
+@findex mc-verify
+This should be a function for verifying that the NoCeM issuer is who she
+says she is. The default is @code{mc-verify}, which is a Mailcrypt
+function. If this is too slow and you don't care for verification
+(which may be dangerous), you can set this variable to @code{nil}.
+
+If you want signed NoCeM messages to be verified and unsigned messages
+not to be verified (but used anyway), you could do something like:
+
+@lisp
+(setq gnus-nocem-verifyer 'my-gnus-mc-verify)
+
+(defun my-gnus-mc-verify ()
+ (not (eq 'forged
+ (ignore-errors
+ (if (mc-verify)
+ t
+ 'forged)))))
+@end lisp
+
+This might be dangerous, though.
+
+@item gnus-nocem-directory
+@vindex gnus-nocem-directory
+This is where Gnus will store its NoCeM cache files. The default is
+@file{~/News/NoCeM/}.
+
+@item gnus-nocem-expiry-wait
+@vindex gnus-nocem-expiry-wait
+The number of days before removing old NoCeM entries from the cache.
+The default is 15. If you make it shorter Gnus will be faster, but you
+might then see old spam.
+
+@item gnus-nocem-check-from
+@vindex gnus-nocem-check-from
+Non-@code{nil} means check for valid issuers in message bodies.
+Otherwise don't bother fetching articles unless their author matches a
+valid issuer; that is much faster if you are selective about the
+issuers.
+
+@item gnus-nocem-check-article-limit
+@vindex gnus-nocem-check-article-limit
+If non-@code{nil}, the maximum number of articles to check in any NoCeM
+group. NoCeM groups can be huge and very slow to process.
+
+@end table
+
+Using NoCeM could potentially be a memory hog. If you have many living
+(i. e., subscribed or unsubscribed groups), your Emacs process will grow
+big. If this is a problem, you should kill off all (or most) of your
+unsubscribed groups (@pxref{Subscription Commands}).
+
+
+@node Undo
+@section Undo
+@cindex undo
+
+It is very useful to be able to undo actions one has done. In normal
+Emacs buffers, it's easy enough---you just push the @code{undo} button.
+In Gnus buffers, however, it isn't that simple.
+
+The things Gnus displays in its buffer is of no value whatsoever to
+Gnus---it's all just data designed to look nice to the user.
+Killing a group in the group buffer with @kbd{C-k} makes the line
+disappear, but that's just a side-effect of the real action---the
+removal of the group in question from the internal Gnus structures.
+Undoing something like that can't be done by the normal Emacs
+@code{undo} function.
+
+Gnus tries to remedy this somewhat by keeping track of what the user
+does and coming up with actions that would reverse the actions the user
+takes. When the user then presses the @code{undo} key, Gnus will run
+the code to reverse the previous action, or the previous actions.
+However, not all actions are easily reversible, so Gnus currently offers
+a few key functions to be undoable. These include killing groups,
+yanking groups, and changing the list of read articles of groups.
+That's it, really. More functions may be added in the future, but each
+added function means an increase in data to be stored, so Gnus will
+never be totally undoable.
+
+@findex gnus-undo-mode
+@vindex gnus-use-undo
+@findex gnus-undo
+The undoability is provided by the @code{gnus-undo-mode} minor mode. It
+is used if @code{gnus-use-undo} is non-@code{nil}, which is the
+default. The @kbd{C-M-_} key performs the @code{gnus-undo}
+command, which should feel kinda like the normal Emacs @code{undo}
+command.
+
+
+@node Predicate Specifiers
+@section Predicate Specifiers
+@cindex predicate specifiers
+
+Some Gnus variables are @dfn{predicate specifiers}. This is a special
+form that allows flexible specification of predicates without having
+to type all that much.
+
+These specifiers are lists consisting of functions, symbols and lists.
+
+Here's an example:
+
+@lisp
+(or gnus-article-unseen-p
+ gnus-article-unread-p)
+@end lisp
+
+The available symbols are @code{or}, @code{and} and @code{not}. The
+functions all take one parameter.
+
+@findex gnus-make-predicate
+Internally, Gnus calls @code{gnus-make-predicate} on these specifiers
+to create a function that can be called. This input parameter to this
+function will be passed along to all the functions in the predicate
+specifier.
+
+
+@node Moderation
+@section Moderation
+@cindex moderation
+
+If you are a moderator, you can use the @file{gnus-mdrtn.el} package.
+It is not included in the standard Gnus package. Write a mail to
+@samp{larsi@@gnus.org} and state what group you moderate, and you'll
+get a copy.
+
+The moderation package is implemented as a minor mode for summary
+buffers. Put
+
+@lisp
+(add-hook 'gnus-summary-mode-hook 'gnus-moderate)
+@end lisp
+
+in your @file{.gnus.el} file.
+
+If you are the moderator of @samp{rec.zoofle}, this is how it's
+supposed to work:
+
+@enumerate
+@item
+You split your incoming mail by matching on
+@samp{Newsgroups:.*rec.zoofle}, which will put all the to-be-posted
+articles in some mail group---for instance, @samp{nnml:rec.zoofle}.
+
+@item
+You enter that group once in a while and post articles using the @kbd{e}
+(edit-and-post) or @kbd{s} (just send unedited) commands.
+
+@item
+If, while reading the @samp{rec.zoofle} newsgroup, you happen upon some
+articles that weren't approved by you, you can cancel them with the
+@kbd{c} command.
+@end enumerate
+
+To use moderation mode in these two groups, say:
+
+@lisp
+(setq gnus-moderated-list
+ "^nnml:rec.zoofle$\\|^rec.zoofle$")
+@end lisp
+
+
+@node Image Enhancements
+@section Image Enhancements
+
+XEmacs, as well as Emacs 21, is able to display pictures and stuff, so
+Gnus has taken advantage of that.
+
+@menu
+* Picons:: How to display pictures of what you're reading.
+* Smileys:: Show all those happy faces the way they were meant to be shown.
+* X-Face:: Display a funky, teensy black-and-white image.
+* XVarious:: Other XEmacsy Gnusey variables.
+@end menu
+
+
+@node Picons
+@subsection Picons
+
+@iftex
+@iflatex
+\include{picons}
+@end iflatex
+@end iftex
+
+So@dots{} You want to slow down your news reader even more! This is a
+good way to do so. Its also a great way to impress people staring
+over your shoulder as you read news.
+
+What are Picons? To quote directly from the Picons Web site:
+
+@iftex
+@iflatex
+\margindex{}
+@end iflatex
+@end iftex
+
+@quotation
+@dfn{Picons} is short for ``personal icons''. They're small,
+constrained images used to represent users and domains on the net,
+organized into databases so that the appropriate image for a given
+e-mail address can be found. Besides users and domains, there are picon
+databases for Usenet newsgroups and weather forecasts. The picons are
+in either monochrome @code{XBM} format or color @code{XPM} and
+@code{GIF} formats.
+@end quotation
+
+@vindex gnus-picon-databases
+For instructions on obtaining and installing the picons databases,
+point your Web browser at
+@uref{http://www.cs.indiana.edu/picons/ftp/index.html}.
+
+If you are using Debian GNU/Linux, saying @samp{apt-get install
+picons.*} will install the picons where Gnus can find them.
+
+To enable displaying picons, simply make sure that
+@code{gnus-picon-databases} points to the directory containing the
+Picons databases.
+
+The following variables offer control over where things are located.
+
+@table @code
+
+@item gnus-picon-databases
+@vindex gnus-picon-databases
+The location of the picons database. This is a list of directories
+containing the @file{news}, @file{domains}, @file{users} (and so on)
+subdirectories. Defaults to @code{("/usr/lib/picon"
+"/usr/local/faces")}.
+
+@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
+@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
+@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 @email{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 @sc{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.