+@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 a specific
+threshold. That threshold can be customized, consult the Bogofilter
+documentation.
+
+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
+
+@table @kbd
+@item M s t
+@itemx S t
+@kindex M s t
+@kindex S t
+@findex spam-bogofilter-score
+Get the Bogofilter spamicity score (@code{spam-bogofilter-score}).
+@end table
+
+@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.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-spam-exit-processor-bogofilter}, it is recommended
+that you use @code{'(spam spam-use-bogofilter)}. Everything will work
+the same way, we promise.
+@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.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-ham-exit-processor-bogofilter}, it is recommended
+that you use @code{'(ham spam-use-bogofilter)}. Everything will work
+the same way, we promise.
+@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 @command{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 @command{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
+
+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 Statistics Filtering
+@subsubsection Spam Statistics Filtering
+@cindex spam filtering
+@cindex spam-stat, spam filtering
+@cindex spam-stat
+@cindex spam
+
+This back end uses the Spam Statistics Emacs Lisp package to perform
+statistics-based filtering (@pxref{Spam Statistics Package}). Before
+using this, you may want to perform some additional steps to
+initialize your Spam Statistics dictionary. @xref{Creating a
+spam-stat dictionary}.
+
+@defvar spam-use-stat
+
+@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.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-spam-exit-processor-stat}, it is recommended
+that you use @code{'(spam spam-use-stat)}. Everything will work
+the same way, we promise.
+@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.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-ham-exit-processor-stat}, it is recommended
+that you use @code{'(ham spam-use-stat)}. Everything will work
+the same way, we promise.
+@end defvar
+
+This enables @file{spam.el} to cooperate with @file{spam-stat.el}.
+@file{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 SpamOracle
+@subsubsection Using SpamOracle with Gnus
+@cindex spam filtering
+@cindex SpamOracle
+@cindex spam
+
+An easy way to filter out spam is to use SpamOracle. SpamOracle is an
+statistical mail filtering tool written by Xavier Leroy and needs to be
+installed separately.
+
+There are several ways to use SpamOracle with Gnus. In all cases, your
+mail is piped through SpamOracle in its @emph{mark} mode. SpamOracle will
+then enter an @samp{X-Spam} header indicating whether it regards the
+mail as a spam mail or not.
+
+One possibility is to run SpamOracle as a @code{:prescript} from the
+@xref{Mail Source Specifiers}, (@pxref{SpamAssassin}). This method has
+the advantage that the user can see the @emph{X-Spam} headers.
+
+The easiest method is to make @file{spam.el} (@pxref{Spam Package})
+call SpamOracle.
+
+@vindex spam-use-spamoracle
+To enable SpamOracle usage by @file{spam.el}, set the variable
+@code{spam-use-spamoracle} to @code{t} and configure the
+@code{nnmail-split-fancy} or @code{nnimap-split-fancy}. @xref{Spam
+Package}. In this example the @samp{INBOX} of an nnimap server is
+filtered using SpamOracle. Mails recognized as spam mails will be
+moved to @code{spam-split-group}, @samp{Junk} in this case. Ham
+messages stay in @samp{INBOX}:
+
+@example
+(setq spam-use-spamoracle t
+ spam-split-group "Junk"
+ nnimap-split-inbox '("INBOX")
+ nnimap-split-rule 'nnimap-split-fancy
+ nnimap-split-fancy '(| (: spam-split) "INBOX"))
+@end example
+
+@defvar spam-use-spamoracle
+Set to @code{t} if you want Gnus to enable spam filtering using
+SpamOracle.
+@end defvar
+
+@defvar spam-spamoracle-binary
+Gnus uses the SpamOracle binary called @file{spamoracle} found in the
+user's PATH. Using the variable @code{spam-spamoracle-binary}, this
+can be customized.
+@end defvar
+
+@defvar spam-spamoracle-database
+By default, SpamOracle uses the file @file{~/.spamoracle.db} as a database to
+store its analysis. This is controlled by the variable
+@code{spam-spamoracle-database} which defaults to @code{nil}. That means
+the default SpamOracle database will be used. In case you want your
+database to live somewhere special, set
+@code{spam-spamoracle-database} to this path.
+@end defvar
+
+SpamOracle employs a statistical algorithm to determine whether a
+message is spam or ham. In order to get good results, meaning few
+false hits or misses, SpamOracle needs training. SpamOracle learns
+the characteristics of your spam mails. Using the @emph{add} mode
+(training mode) one has to feed good (ham) and spam mails to
+SpamOracle. This can be done by pressing @kbd{|} in the Summary
+buffer and pipe the mail to a SpamOracle process or using
+@file{spam.el}'s spam- and ham-processors, which is much more
+convenient. For a detailed description of spam- and ham-processors,
+@xref{Spam Package}.
+
+@defvar gnus-group-spam-exit-processor-spamoracle
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameter 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
+sent to SpamOracle as spam samples.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-spam-exit-processor-spamoracle}, it is recommended
+that you use @code{'(spam spam-use-spamoracle)}. Everything will work
+the same way, we promise.
+@end defvar
+
+@defvar gnus-group-ham-exit-processor-spamoracle
+Add this symbol to a group's @code{spam-process} parameter by
+customizing the group parameter 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 sent to the SpamOracle as samples of ham
+messages. Note that this ham processor has no effect in @emph{spam} or
+@emph{unclassified} groups.
+
+@emph{WARNING}
+
+Instead of the obsolete
+@code{gnus-group-ham-exit-processor-spamoracle}, it is recommended
+that you use @code{'(ham spam-use-spamoracle)}. Everything will work
+the same way, we promise.
+@end defvar
+
+@emph{Example:} These are the Group Parameters of a group that has been
+classified as a ham group, meaning that it should only contain ham
+messages.
+@example
+ ((spam-contents gnus-group-spam-classification-ham)
+ (spam-process ((ham spam-use-spamoracle)
+ (spam spam-use-spamoracle))))
+@end example
+For this group the @code{spam-use-spamoracle} is installed for both
+ham and spam processing. If the group contains spam message
+(e.g. because SpamOracle has not had enough sample messages yet) and
+the user marks some messages as spam messages, these messages will be
+processed by SpamOracle. The processor sends the messages to
+SpamOracle as new samples for spam.
+
+@node Extending the Spam package
+@subsection Extending the Spam 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