No - I'm not an answering script ...
Group: Admin
Posts: 6631
Member No.: 195
Joined: 19-June 02
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One of XMail's ost powerful features are filters. To make things more clear, here the mail flow schemata, when and how messages are filtered:
Receiving or sending mail via SMTP:
- During SMTP conversation: filters.pre-data.tab
- Before ending the SMTP dialog: filters.post-data.tab
- Now the mail's envelope is removed and the spoolfile is generated.
- If the mail contains multiple RCPT_TO or CC and BCC recipients, further spoolfiles are generated for each recipient .
Those spoolfiles take the following routes now:
- If the recipient is local, it runs through filters.in.tab
- Otherwise, it travels through filters.out.tab
Receiving mail via pop3links.tab:
- These mails go directly through filters.in.tab
Sending mail vial local mailer /spool/local:
- Depending on the recipient, these mails go through filters.in.tab (local) or filters.out.tab (external)
For more details about filters read these 2 sections in the manual:
| QUOTE |
SMTP MESSAGE FILTERS
Besides having the ability to perform off-line message filtering, XMail
gives the user the power to run filters during the SMTP session. Two
files drive the SMTP on-line filtering, and these are
'FILTERS.PRE-DATA.TAB' and 'FILTERS.POST-DATA.TAB'. The file
'FILTERS.PRE-DATA.TAB' contains one or more commands to be executed
after the remote SMTP client sends the DATA command, and before XMail
sends the response to the command. Using such filters, the user can tell
XMail if or if not accept the following DATA transaction and, in case of
rejection, the user is also allowed to specify a custom message to be
sent to the remote SMTP client. The file 'FILTERS.POST-DATA.TAB'
contains one or more commands to be executed after XMail received the
whole client DATA, and before XMail sends the final response to the DATA
command (final messages ack). The files 'FILTERS.PRE-DATA.TAB' and
'FILTERS.POST-DATA.TAB' conatins zero or more lines with the following
format:
"command"[TAB]"arg-or-macro"[TAB]...[NEWLINE]
Each file may contain multiple commands, that will be executed in
strictly sequential order. The first command that will trigger a
rejection code will make the filtering process to end. Each argument can
be a macro also:
@@FILE
message file path
@@USERAUTH
name of the SMTP authenticated user, or "-" if not authentication
has been granted
@@REMOTEADDR
remote IP address and port of the sender
@@LOCALADDR
local IP address and port where the message has been accepted
Filter commands have the ability to inspect and modify the content of
the message (or info) file. The exit code of commands executed by XMail
are used to tell XMail the action that has to be performed as a
cosequence of the filter. The exit code is composed by a raw exit code
and additional flags. Currently defined flags are:
'16'
Stop selected filter list processing.
Currently defined raw exit codes are:
'3' Reject the message.
Any other exit codes will make XMail to accept the message, and can be
used also when changing the content of the @@FILE file. 'EXTREME' care
must be used when changing the @@FILE file, since XMail expect the file
format to be correct. Also, it is important to preserve the <CR><LF>
line termination of the file itself. When rejecting the message, the
filter command has the ability to specify the SMTP status code that
XMail will send to the remote SMTP client, by creating a file named
@@FILE.rej containing the message in the very first line. Such file will
be automatically removed by XMail. The data passed to filter commands
inside @@FILE varies depending if the command is listed inside
'FILTERS.PRE-DATA.TAB' or inside 'FILTERS.POST-DATA.TAB'. Commands
listed inside 'FILTERS.PRE-DATA.TAB' will receive the following data
stored inside @@FILE:
Info Data [ 1th line ]
SmtpDomain [ 2nd line ]
SmtpMessageID [ 3rd line ]
MAIL FROM:<...> [ 4th line ]
RCPT TO:<...> {...} [ 5th line ]
...
The file can have one or more "RCPT TO" lines. The format of the "Info
Data" line is:
ClientDomain;ClientIP;ClientPort;ServerDomain;ServerIP;ServerPort;Time;Logo
Commands listed inside 'FILTERS.POST-DATA.TAB' will receive the
following data stored inside @@FILE:
Info Data [ 1th line ]
SmtpDomain [ 2nd line ]
SmtpMessageID [ 3rd line ]
MAIL FROM:<...> [ 4th line ]
RCPT TO:<...> {...} [ 5th line ]
...
<<MAIL-DATA>>
...
After the '<<MAIL-DATA>>' tag the message follows. The message is
composed of a headers section and, after the first empty line, the
message body. The format of the RCPT line is:
RCPT TO:<address> {ra=real-address}
where "real-address" is the "address" after it has been translated (if
aliases applies) to the real local address. Otherwise it holds the same
value of "address".
|
| QUOTE |
MESSAGE FILTERS
This feature offers a way to filter messages by providing the ability to
execute external programs, such as scripts or real executables. These
'filters' may examine and/or modify messages and inform XMail of their
actions with a return value.
This feature offers the ability to inspect and modify messages, giving a
way to reject messages based on content, alter messages (address
rewriting) and so on.
If this filters returns '4, 5 or 6' the message is rejected and is
stopped in its travel. If the filter modifies the message it must return
'7'.
Additional flags are allowed to be returned to XMail as a result of
filter processing by adding the flags value to the exits code above
listed. The currently defined flags are :
'16'
Stop selected filter list processing.
Filter flags are additive and if more than one flag need to be
specified, their values must be added together. If a filter "raw" exit
code is RC and the filter needs to return extra flags FILTER-SUM, the
final return code FRC must be :
FRC = RC + FILTER-SUM
Example. Suppose a filter modified the message and hence needs to return
7 as return code. Suppose also that a filter wants to block the filter
selection list processing by specifying a flags value of 16, the value
to be returned will be :
FRC = 7 + 16 = 23
Filter selection is driven by two files 'FILTERS.IN.TAB' and
'FILTERS.OUT.TAB' located inside the $MAIL_ROOT/ directory and that have
the following format:
"sender"[TAB]"recipient"[TAB]"remote-addr"[TAB]"local-addr"[TAB]"filename"[NEWLINE]
For example:
"*@bad-domain.com" "*" "0.0.0.0/0" "0.0.0.0/0" "av-filter.tab"
"*" "clean@purified.net" "0.0.0.0/0" "0.0.0.0/0" "spam-block.tab"
"*" "*" "192.168.1.0/24" "0.0.0.0/0" "archive.tab"
where the file "av-filter.tab" must be present inside the
$MAIL_ROOT/filters directory. The "sender" and the "recipient" are
resolved to the real account when possible. Address selection mask are
formed by an IP address (network) plus the number of valid bits inside
the network mask. The file 'FILTERS.IN.TAB' lists filters that have to
be applied to inbound messages (going to local mailboxes) while the file
'FILTERS.OUT.TAB' lists filters that have to be applied to outbound
messages (delivered remotely). All four
(sender+recipient+remote-addr+local-addr) selection fields must have a
match in order "filename" to be evaluated. The syntax of the filter file
is:
"command"[TAB]"arg-or-macro"[TAB]...[NEWLINE]
Each file may contain multiple commands, that will be executed in
strictly sequential order. The first command that will trigger a
rejection code will make the filtering process to end. Each argument can
be a macro also:
@@FROM
the sender of the message
@@RFROM
the sender of the message resolved to the real account, when
possible (alias resolution)
@@RCPT
the target of the message
@@RRCPT
the target of the message resolved to the real account, when
possible (alias resolution)
@@REMOTEADDR
remote IP address and port of the sender
@@LOCALADDR
local IP address and port where the message has been accepted
@@FILE
the message file path (the external command may modify the file if
it returns '7' as command exit value.)
@@MSGID
with the (XMail unique) message id
@@MSGREF
the reference SMTP message id
Here 'command' is the name of an external program that processes the
message and returns its processing result. If it returns '6' the message
is rejected and a notification message is sent to the sender. By
returning '5' the message is rejected without notification. While
returning '4' the message is rejected without notification and without
being frozen (a '5' response could lead to a frozen message if the
"SERVER.TAB" configuration enables this). If all filters return values
different from '6, 5 and 4' the message continues its trip. The filter
command may also modify the file (AV scanning, content filter, message
rewriting, etc) by returning '7'. The filter 'MUST' return '7' in case
it modifies the message. If the filter changes the message file it
'MUST' keep the message structure and it 'MUST' terminate all line with
<CR><LF>. The filter has also the ability to return a one-line custom
return message by creating a file named @@FILE.rej holding the message
in the very first line. This file should be created 'ONLY' when the
filter returns a rejection code ('6, 5 and 4')and 'NEVER' in case of
passthru code ('7') or modify code.
The spool files has this structure:
Info Data [ 1th line ]
SmtpDomain [ 2nd line ]
SmtpMessageID [ 3rd line ]
MAIL FROM:<...> [ 4th line ]
RCPT TO:<...> [ 5th line ]
<<MAIL-DATA>> [ 6th line ]
...
After the '<<MAIL-DATA>>' tag (5th line) the message follows. The
message is composed of a headers section and, after the first empty
line, the message body. The format of the "Info Data" line is:
ClientDomain;ClientIP;ClientPort;ServerDomain;ServerIP;ServerPort;Time;Logo
'EXTREME' care must be used when modifying the message because the
filter will be working on the real message, and a badly reformatted file
will lead to message loss. The spool file header (any data before
<<MAIL-DATA>>) 'MUST' be preserved as is by the filter in case of
message rewrite happens.
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Xmail's Filter Mechanism, How mail flows though the filters
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