gnus: Filtering Incoming Mail
9.17.2 Filtering Incoming Mail
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To use the Spam package to filter incoming mail, you must first set up
fancy mail splitting. 
Fancy Mail Splitting. The Spam package
defines a special splitting function that you can add to your fancy
split variable (either ‘nnmail-split-fancy’ or ‘nnimap-split-fancy’,
depending on your mail back end):
(: spam-split)
The ‘spam-split’ function scans incoming mail according to your chosen
spam back end(s), and sends messages identified as spam to a spam group.
By default, the spam group is a group named ‘spam’, but you can change
this by customizing ‘spam-split-group’. Make sure the contents of
‘spam-split-group’ are an unqualified group name. For instance, in an
‘nnimap’ server ‘your-server’, the value ‘spam’ means
‘nnimap+your-server:spam’. The value ‘nnimap+server:spam’ is therefore
wrong—it gives the group ‘nnimap+your-server:nnimap+server:spam’.
‘spam-split’ does not modify the contents of messages in any way.
Note for IMAP users: if you use the ‘spam-check-bogofilter’,
‘spam-check-ifile’, and ‘spam-check-stat’ spam back ends, you should
also set the variable ‘nnimap-split-download-body’ to ‘t’. These spam
back ends are most useful when they can “scan” the full message body.
By default, the nnimap back end only retrieves the message headers;
‘nnimap-split-download-body’ tells it to retrieve the message bodies as
well. We don’t set this by default because it will slow IMAP down, and
that is not an appropriate decision to make on behalf of the user.
Client-Side IMAP Splitting.
You have to specify one or more spam back ends for ‘spam-split’ to
use, by setting the ‘spam-use-*’ variables. Spam Back Ends.
Normally, ‘spam-split’ simply uses all the spam back ends you enabled in
this way. However, you can tell ‘spam-split’ to use only some of them.
Why this is useful? Suppose you are using the ‘spam-use-regex-headers’
and ‘spam-use-blackholes’ spam back ends, and the following split rule:
nnimap-split-fancy '(|
(any "ding" "ding")
(: spam-split)
;; default mailbox
"mail")
The problem is that you want all ding messages to make it to the ding
folder. But that will let obvious spam (for example, spam detected by
SpamAssassin, and ‘spam-use-regex-headers’) through, when it’s sent to
the ding list. On the other hand, some messages to the ding list are
from a mail server in the blackhole list, so the invocation of
‘spam-split’ can’t be before the ding rule.
The solution is to let SpamAssassin headers supersede ding rules, and
perform the other ‘spam-split’ rules (including a second invocation of
the regex-headers check) after the ding rule. This is done by passing a
parameter to ‘spam-split’:
nnimap-split-fancy
'(|
;; spam detected by ‘spam-use-regex-headers’ goes to ‘regex-spam’
(: spam-split "regex-spam" 'spam-use-regex-headers)
(any "ding" "ding")
;; all other spam detected by spam-split goes to ‘spam-split-group’
(: spam-split)
;; default mailbox
"mail")
This lets you invoke specific ‘spam-split’ checks depending on your
particular needs, and target the results of those checks to a particular
spam group. You don’t have to throw all mail into all the spam tests.
Another reason why this is nice is that messages to mailing lists you
have rules for don’t have to have resource-intensive blackhole checks
performed on them. You could also specify different spam checks for
your nnmail split vs. your nnimap split. Go crazy.
You should set the ‘spam-use-*’ variables for whatever spam back ends
you intend to use. The reason is that when loading ‘spam.el’, some
conditional loading is done depending on what ‘spam-use-xyz’ variables
you have set. Spam Back Ends.
Info Catalog
gnus: Spam Package Introduction
gnus: Spam Package
gnus: Detecting Spam in Groups