This filter system should give sufficient flexibility so that most common requirements in terms of blocking individual spammers and blocking new email virus plague's in a hurry.
Fast processing of incoming messages.
A simple clear syntax so rules can easily be understood and modified
Enough power/flexibility
Incorporate regular expression matching.
Not to create a new elaborate language if possible.
There are 5 valid statements in a rule file:
Assignment
Action
if (Conditional_Expression) [and (Conditional_Expression)...] Action
else
end if
Assignment
$variable_name = "quoted string" [+ "quoted string"
[+ $variable ...]]
Action
accept "reason" | bounce "reason" | drop
"reason" | forward "user@domain" | then
| setflag("flagname") | clearflag("flagname")
Conditional_Expression
Any pre defined function, e.g. isbinary(),
isin("subject","free pictures")
Numeric comparisons, e.g. lines()>100
Simple NOT operator, e.g. if (!isbinary()) reject "Only binaries
alowed here mate!"
Calculations are NOT permitted, e.g. lines()+10 would fail
Line continuation
Lines can be continue by ending the line in a '\' character
Quoting strings
All strings and header names should be within double quotes, sometimes
you may get away without doing this, but we don't gaurantee this will work in future.
e.g. use: exists("Supersedes") not exists(Supersedes), quotes can
be escaped in the usual way, e.g. "This \"Word\" has quotes around it"
Assignments are processed at compile time, variables DO NOT exist at run time.
Don't think of this as a programming language, but rather as a list of rules that are
processed with each incoming message. Real run-time variables only exist in the form of
the ifflag("xxx") function and the setflag("xxx") action.
For example the following is NOT VALID, as the assignment is processed before the rules
are run. The rejection would always read "big message"
$fred = "small message"
if (lines()>100) then
$fred = "big message" (this will not
work as expected)
end if
reject $fred
forward_cc("new@email.address)
replace("header_name","wildcard_match_pattern","replacement_pattern")
report("manger@email.address","subject of message")
isin("header","string-not-case-sensitive")
rexp("header","regular-expression")
match("header","wildcard")
size()
matchall("header","wildcardlist")
matchone("header","wildcardlist")
ifflag("flag-name")
exists("header")
isbinary()
ishtml()
isencodedhtml()
isencodedtext()
isencodedurl()
isbase64()
isimage()
lines()
allmod()
tellsmtp mfilter_test d:\test.msg d:\test.rul
If the named header matches the 'wildcard_match_pattern' then the replacement pattern is applied, e.g.
replace("from",,"*@*.domain.name","BOB_$1@$2.other.name")
Subject: "joe@this.domain.name"
Would be translated to:
Subject: "BOB_joe@this.other.name"
Sends an email including the top part of the offending message to the specified person, with the specified subject, this is intended when you want to be alerted to something but don't want to simply forward the message itself which may be 'confusing' as it would look like the message had been sent to the manager directly.
Sends the current message to this new email address in addition to any existing desitination users.
This is a simple 'content' searching function, if the named header contains the string (a non case sensitive match is used) e.g.
if (isin("Subject","Free")) reject "Probably a spammer selling something"
This would reject a message containing a subject of "Get your Free pictures here", it would also reject a message containing a subject of "Is there any real freedom in the world?" so it's probably not a good rule :-)
This function searches the named header for a regular expression, the matching is not case sensitive, use rexp_case() for a case sensitive version.
This function applies a simple wild card matching algorithym as is typically used to match file names, e.g. match("From","*@netwin.co.nz*") would match against a message from that domain.
Returns the size in bytes of the current message, can be used with > and < operators.
Used for matching a single wild card, against a header which contains a list of values, like Newsgroups:, Path:, etc..., The match is TRUE only if all entries in the list match, e.g. if (matchall("Newsgroups","news.filters.*")) accept "It is only in the filters list so we will accept it"
Identical to the above function, but returns 'TRUE' if any match occurs.
Used to check if a flag variable has been defined as true, this can be done with the setflag("flag-name") action, e.g.
if (size()>100000) setflag("bigitem") if (isimage()) setflag("bigitem") if (isflag("bigitem")>100000) reject "It was a big item or had a picture in it"
This is true if the header exists in the message and is non zero in length, e.g. if (exists("supersedes")) then reject "We don't like supersedes headers"
This is true if the message has binary data, either base64 encoding or uuencoded data.
This is true if the message appears to contain HTML instead of plain text data.
This is true if the message appears to contain mime or uuencoded HTML instead of plain text data.
This is true if the message appears to contain mime or uuencoded text data. This will always be true if isencodedhtml() returns true.
This is true if the message appears to contain a uuencoded URL reference.
This is true if the message appears to contain base64 binary encoded data.
This is true if the message appears to contain a picture (either mime or uuencoded)
This returns the number of lines in the message.
This returns true if all the newsgroups in the specified header are moderated.
Actions
accept "reason"
Accepts the current article reporting the "reason" specified in the log files.
reject "reason"
Rejects the current article reporting the "reason" specified in the log files.
setflag("flag-name")
Used to set the specified flag variable to the true state.
clearflag("flag-name")
Used to set the specified flag variable to the false state.
Specials:
\s = white space
\S = not white space
\d = digit
\D = not digit
\b = word boundary
\B = not word boundary
\x00 = Hex character
. (period) represents any one character.
[] (brackets) contain a set of characters from which a match can be made. It corresponds
to one character in the search string.
\ (backslash) is an escape character which means that the next character will not have a
special meaning.
* (asterisk) is a multiplier. It will match zero or more ofthe previous character. (Note
that it's not a wildcard character as in file names.)
? (question mark) is a multiplier. It will match zero or one of the previous character.
(Note that it's not a wildcard character as in file names.)
+ (plus) is a multiplier. It will match one or more of the previous character.
{} (squiggly brackets) contain a number which specifies an exact number of the previous
character. Or range {2,3}
[^] (brackets containing caret and other characters) means any characters except the
character(s) after the caret symbol
in the brackets.
^ (caret) is the start of the line.
$ (dollar) is the end of the line.
\< represents the start of a word.
\> represents the end of a word.
[:alpha:] represents any alphabetic letter.
[:digit:] represents any single-digit number.
[:blank:] represents a space or tab.
| (pipe) is OR. It requires that the joined expressions have parentheses around them.
Examples:
e.a matches eta, eda, e1a, but not Eta
[eE].a matches eta and Eta
E.*a matches Eudora, Etcetera, Ea
ho+p matches hop, hoop, hoooop, but not hp
etc\. matches etc. but not etc
Lookahead operator
Free(?!dom|bsd) matches freesex but not freedom or freebsd
$sex = "fuck|xxx|sex" $free = "free(?!dom|bsd|nix|serve)" $pics = "pi[cx]" $free_pictures = $free + $pics $bad_guys = + "|freepictures|jus.?.?\.doi.?.?\.to|great\.site|webbinaries" \ + "|yad.?.?.?\.ion.?.?\.org|freehidden|joy.?.?\.to.?.?\.al|from.?behind" \ + "|love(youhon|ergirl|chatting|stofuck)|forever\.yours|\@ju.?.?\.sex|town.\girl|beachbums" \i
# Do some processing which is specific to individual recipients recipients if (isin("recipient","manager@this.domain")) accept "Always accept for me so spammers can talk to me" if (isin("recipient","sales@your.domain")) then if (isin("subject","order")) then call forward_cc("sales_copy@your.domain","Duplicate of order") endif endif end recipients
# Check for some known spammers and naughty subjects if (rexp(subject,$free_pictures)) bounce "No emails about free pictures" if (rexp(from,$bad_guys)) bounce "No emails from black listed people thanks" # Strip local node names from from addresses: call replace("From","*@*.parts.co.nz","$1@parts.co.nz")
accept "Great, we liked the message"