FILTER(1) FILTER(1)
NAME
filter, list, deliver, token, vf - filtering mail
SYNOPSIS
upas/filter [ -bh ] rcvr mailbox [ regexp file ] ...
upas/list [ -d ] add|check patternfile addressfile ...
upas/deliver recipient fromfile mbox
upas/dkim [ -d domain ] [ -s selector ]
upas/token key [ tokenfile ]
upas/vf [ -r ] [ -s savefile ]
DESCRIPTION
A user may filter all incoming mail by creating a world
readable/executable file /mail/box/username/pipeto. If the
file is a shell script, it can use the commands described
here to implement a filter.
Filter provides simple mail filtering. The first two argu-
ments are the recipient's address and mailbox, that is, the
same arguments provided to pipeto. The remaining arguments
are all pairs of a regular expression and a file name. With
no flags, the sender's address is matched against each regu-
lar expression starting with the first. If the expression
matches, then the message is delivered to the file whose
name follows the expression. The file must be world writ-
able and should be append only. A message that matches none
of the expressions is delivered into the user's standard
mail box.
By default, filter matches each regular expression against
the message's sender. The -h flag causes filter to match
against the entire header, and the -b flag causes filter to
match against the entire message (header and body).
For example, to delete any messages of precedence bulk,
place in your pipeto file:
/bin/upas/filter -h $1 $2 'Precedence: bulk' /dev/null
Three other commands exist which, combined by an rc(1)
script, allow you to build your own filter.
List takes two verbs; check and add. Check directs list to
check each address contained in the addressfiles against a
list of patterns in patternfile. Patterns come in four
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forms:
~regular-expression If any address matches the regular
expression, list returns successfully.
=string. If any address exactly matches string,
list returns successfully.
!~regular-expression If any address matches the regular
expression and no other address matches
a non `!' rule, list returns error sta-
tus "!match".
!=string If any address exactly matches string
and no other address matches a non `!'
rule, list returns error status
"!match".
If no addresses match a pattern, list returns "no match".
The pattern file may also contain lines of the form
#include filename
to allow pattern files to include other pattern files. All
pattern matches are case insensitive. List searches the
pattern file (and its includes) in order. The first match-
ing pattern determines the action.
List add directs list to add a pattern to patternfile for
each address in the addressfiles that doesn't already match
a pattern.
Token, with only one argument, prints to standard output a
unique token created from the current date and key. With two
arguments, it checks token against tokens created over the
last 10 days with key. If a match is found, it returns suc-
cessfully.
Deliver delivers into mail box mbox the message read from
standard input. It obeys standard mail file locking and
logging conventions.
/sys/src/cmd/upas/filterkit/pipeto.sample is a sample pipeto
using the filter kit.
A sample pipefrom,
/sys/src/cmd/upas/filterkit/pipefrom.sample, is provided
which adds all addresses of your outgoing mail to your pat-
tern file. You should copy it into a directory that nor-
mally gets bound by your profile onto /bin.
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Dkim Takes a mail message as standard input, and signs a
selection of headers and the body of the message. The -d
flag specifies the domain, and the -s flag specifies the
selector. If the selector is not specified, it defaults to
dkim. The keyspec searched for the signing key is:
proto=rsa service=dkim role=sign hash=sha256 domain=$domain
Vf (virus filter) takes a mail message as standard input and
searches for executable MIME attachments, either rewriting
them to be non-executable or rejecting the message. The
behavior depends on the attachment's file name extension and
MIME content type. /sys/lib/mimetype contains the list of
known extensions and MIME content types. The fifth field of
each line specifies the safety of a particular file type: y
(yes), m (maybe; treated same as yes), n (no), p (previous),
or r (reject). Vf allows attachments with safety y or m to
pass through unaltered. Attachments with safety n both are
wrapped in extra MIME headers and have .suspect appended to
their file names, to avoid automatic execution by mail read-
ers. Attachments with safety r (currently, .bat, .com,
.exe, and .scr, all Microsoft executable extensions) are
taken as cause for the entire message to be rejected. A
safety of p (used for the x-gunzip mime type) causes the
previous extension to be tested, so that x.tar.gz is treated
the same as x.tar.
If /mail/lib/validateattachment exists and is executable, vf
runs it on all attachments with safety n (attachments it
would normally sanitize). If validateattachment's exit sta-
tus contains the string `discard', vf rejects the entire
message. If the status contains the string `accept', vf
does not sanitize the attachment. Otherwise, vf sanitizes
the attachment as before. The standard validateattachment
uses file(1) to determine the file type. It accepts text
and image files and discards messages containing executables
or zip (see gzip(1)) archives of executables.
The -r option causes vf not to sanitize MIME attachments,
but instead to reject messages it determines to be viruses.
The -s option causes vf to log all attachments of safety r
in the mail box savefile.
FILES
/mail/box/*/pipeto mail filter
/sys/lib/mimetype MIME content types
/mail/lib/validateattachment attachment checker
SOURCE
/sys/src/cmd/upas/send
/sys/src/cmd/upas/filterkit
/sys/src/cmd/upas/vf
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SEE ALSO
aliasmail(8), faces(1), mail(1), marshal(1), mlmgr(1),
nedmail(1), qer(8), rewrite(6), send(8), smtp(8), upasfs(4)
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