postfix milter简介

Milter介绍

•Sendmail Content Management API

•Open source Sendmail 8.12 and later

•Postfix 2.3开始支持Milter协议

•Postfix 2.4支持sendmail 8.13.0所有的请求接口

Postfix2.6后支持所有sendmail 8.14.0所有请求接口

功能

•enables third-party programs to access mail messages as theyare being processed by the Mail Transfer Agent (MTA)

• allows them to examine and modify message content andmeta-information during the SMTP transaction

SMTP 和milter对应

SMTP Commands	Milter Callbacks
(open SMTP connection)	xxfi_connect
HELO ...	xxfi_helo
MAIL From: ...	xxfi_envfrom
RCPT To: ...	xxfi_envrcpt
[more RCPTs]	[xxfi_envrcpt]
DATA	xxfi_data
Header: ...	xxfi_header
[more headers]	[xxfi_header]
	xxfi_eoh
body...	xxfi_body
[more body...]	[xxfi_body]
.	xxfi_eom
QUIT	xxfi_close

工作原理

For each of N connections

{

        For each filter

                processconnection (xxfi_connect)

        For each filter

                processhelo (xxfi_helo)

MESSAGE:For each message in thisconnection (sequentially)

        {

                Foreach filter

                       process sender (xxfi_envfrom)

                Foreach recipient

                {

                       For each filter

                                processrecipient (xxfi_envrcpt)

                }

                Foreach filter

                {

                       process DATA (xxfi_data)

                       For each header

                                process header(xxfi_header)

                       process end of headers (xxfi_eoh)

                       For each body block

                                process thisbody block (xxfi_body)

                       process end of message (xxfi_eom)

                }

        }

        For each filter

                processend of connection (xxfi_close)

}

•The lifetime of a connection is bracketed by calls to thecallbacksxxfi_connectandxxfi_close

•Each message is bracketed by calls to xxfi_envfrom andxxfi_eom (or xxfi_abort)

API

•Library Control Functions

Function	Description
smfi_opensocket	Try to create the interface socket.
smfi_register	Register a filter.
smfi_setconn	Specify socket to use.
smfi_settimeout	Set timeout.
smfi_setbacklog	Define the incoming listen(2) queue size.
smfi_setdbg	Set the milter library debugging (tracing) level.
smfi_stop	Cause an orderly shutdown.
smfi_main	Hand control to libmilter.

•Data Access Functions

Function	Description
smfi_getsymval	Return the value of a symbol.
smfi_getpriv	Get the private data pointer.
smfi_setpriv	Set the private data pointer.
smfi_setreply	Set the specific reply code to be used.
smfi_setmlreply	Set the specific multi-line reply to be used.

•Message Modification Functions

Function	Description	SMFIF_* flag
smfi_addheader	Add a header to the message.	SMFIF_ADDHDRS
smfi_chgheader	Change or delete a header.	SMFIF_CHGHDRS
smfi_insheader	Insert a header into the message.	SMFIF_ADDHDRS
smfi_chgfrom	Change the envelope sender address.	SMFIF_CHGFROM
smfi_addrcpt	Add a recipient to the envelope.	SMFIF_ADDRCPT
smfi_addrcpt_par	Add a recipient including ESMTP parameter to the envelope.	SMFIF_ADDRCPT_PAR
smfi_delrcpt	Delete a recipient from the envelope.	SMFIF_DELRCPT
smfi_replacebody	Replace the body of the message.	SMFIF_CHGBODY

•Callbacks

Function	Description
xxfi_connect	connection info
xxfi_helo	SMTP HELO/EHLO command
xxfi_envfrom	envelope sender
xxfi_envrcpt	envelope recipient
xxfi_data	DATA command
xxfi_unknown	Unknown SMTP command
xxfi_header	header
xxfi_eoh	end of header
xxfi_body	body block
xxfi_eom	end of message
xxfi_abort	message aborted
xxfi_close	connection cleanup
xxfi_negotiate	option negotiattion

•Other Message Handling Functions

Function	Description
smfi_progress	Report operation in progress.
smfi_quarantine	Quarantine a message.

•Miscellaneous

Function	Description
smfi_version	libmilter (runtime) version info
smfi_setsymlist	Set the list of macros that the milter wants to receive from the MTA for a protocol stage.

return value

Return value

SMFIS_CONTINUE

Continue processing the current connection, message, or recipient.

SMFIS_REJECT

For a connection-oriented routine, reject this connection; callxxfi_close.

For a message-oriented routine (except xxfi_eom orxxfi_abort), reject this message.

For a recipient-oriented routine, reject the current recipient (but continue processing the current message).

SMFIS_DISCARD

For a message- or recipient-oriented routine, accept this message, but silently discard it.

SMFIS_DISCARD should not be returned by a connection-oriented routine.

SMFIS_SKIP

Skip further callbacks of the same type in this transaction. Currently this return value is only allowed in xxfi_body(). It can be used if a milter has received sufficiently many body chunks to make a decision, but still wants to invoke message modification functions that are only allowed to be called from xxfi_eom(). Note: the milter must negotiate this behavior with the MTA, i.e., it must check whether the protocol action SMFIP_SKIP is available and if so, the milter must request it.

SMFIS_NOREPLY

Do not send a reply back to the MTA. The milter must negotiate this behavior with the MTA, i.e., it must check whether the appropriate protocol action SMFIP_NR_* is available and if so, the milter must request it. If you set the SMFIP_NR_* protocol action for a callback, that callback must always reply with SMFIS_NOREPLY. Using any other reply code is a violation of the API. If in some cases your callback may return another value (e.g., due to some resource shortages), then you must not set SMFIP_NR_* and you must use SMFIS_CONTINUE as the default return code. (Alternatively you can try to delay reporting the problem to a later callback for which SMFIP_NR_* is not

SMFIS_ACCEPT

For a connection-oriented routine, accept this connection without further filter processing; call xxfi_close.

For a message- or recipient-oriented routine, accept this message without further filtering.

SMFIS_TEMPFAIL

Return a temporary failure, i.e., the corresponding SMTP command will return an appropriate 4xx status code. For a message-oriented routine (except xxfi_envfrom), fail for this message.

For a connection-oriented routine, fail for this connection; call xxfi_close.

For a recipient-oriented routine, only fail for the current recipient; continue message processing.