Using spam.el and spam-stat.el with an nnimap backend.

I previously had a group called "spam", which is the default
spam group for spam.el. Otherwise I guess you need to create
this.

All my mails start in INBOX, I then split mails with
nnimap-split-fancy to email list groups and to the "spam"
group based on a corporate spam filter. The emails that
are left are put in "incoming".

I did the following changes

in .emacs:

(load "spam")

in gnus.el add this rule to nnimap-split-fancy:
   (: spam-split)

Customize:
 '(spam-use-stat t)
 '(gnus-spam-process-destinations (quote (("incoming" "spam"))))

Train spam-stat:

Start from scratch: (spam-stat-reset)
Reset:(setq spam-stat (make-hash-table :test 'equal))
Learn spam: (spam-stat-process-spam-directory "~/News/agent/nnimap/mailse01.axis.se/spam")
Learn non-spam:
(spam-stat-process-non-spam-directory "~/News/agent/nnimap/mailse01.axis.se/incoming")
(spam-stat-process-non-spam-directory "~/News/agent/nnimap/mailse01.axis.se/INBOX_Archive")
(spam-stat-process-non-spam-directory "~/News/agent/nnimap/mailse01.axis.se/INBOX_Personal")
(spam-stat-process-non-spam-directory "~/News/agent/nnimap/mailse01.axis.se/lists_ding")

Reduce table size: (spam-stat-reduce-size)
Save table: (spam-stat-save)

Then I customized group parameters for the "incoming" group
containing ham mails as such:

 (spam-contents gnus-group-spam-classification-ham)
 (spam-process
  (gnus-group-ham-exit-processor-stat))

and for the spam group:

 (spam-contents gnus-group-spam-classification-spam)
 (spam-process
  (gnus-group-spam-exit-processor-stat))
 (ham-process-destination . "incoming")

and that's it.

When spam end up in ham groups I just press M-d and the
stats are updated when exiting the group.