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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/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 arguments 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 regular 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 writable 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 forms:

If any address matches the regular expression, list returns successfully.  

If any address exactly matches string, list returns successfully.  

If any address matches the regular expression and no other address matches a non ‘!’ rule, list returns error status "!match".  

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 matching 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 successfully.

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 pattern file. You should copy it into a directory that normally gets bound by your profile onto /bin.

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 readers. 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 status 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 filter  

MIME content types  

attachment checker  

SOURCE

/sys/src/cmd/upas/send
/sys/src/cmd/upas/filterkit
/sys/src/cmd/upas/vf

SEE ALSO

aliasmail(8), faces(1), mail(1), marshal(1), mlmgr(1), nedmail(1), qer(8), rewrite(6), send(8), smtp(8), upasfs(4)