Postfix before-queue Milter support

Milter == Mail Filter，一种邮件过滤协议，用于在mta以外的程序对smtp的每个事件进行注入，在邮件进入队列以前判断邮件是否容许发送，检查邮件签名等。要使用milter，能够在main.cf中作以下配置：

1 /etc/postfix/main.cf:
2     smtpd_milters = { inet:host:port,
3         connect_timeout=10s, default_action=accept }

postfix模拟了一些与Sendmail相似的宏，这些宏能够在邮件发送的不一样阶段使用：

Sendmail macro	Milter protocol stage	Description
i	DATA, EOH, EOM	Queue ID, also Postfix queue file name
j	Always	Value of myhostname
_	Always	The validated client name and address
{auth_authen}	MAIL, DATA, EOH, EOM	SASL login name
{auth_author}	MAIL, DATA, EOH, EOM	SASL sender
{auth_type}	MAIL, DATA, EOH, EOM	SASL login method
{client_addr}	Always	Remote client IP address
{client_connections}	CONNECT	Connection concurrency for this client (zero if the client is excluded from all smtpd_client_* limits).
{client_name}	Always	Remote client hostname  When address → name lookup or name → address verification fails: "unknown"
{client_port}	Always (Postfix ≥2.5)	Remote client TCP port
{client_ptr}	CONNECT, HELO, MAIL, DATA	Client name from address → name lookup  When address → name lookup fails: "unknown"
{cert_issuer}	HELO, MAIL, DATA, EOH, EOM	TLS client certificate issuer
{cert_subject}	HELO, MAIL, DATA, EOH, EOM	TLS client certificate subject
{cipher_bits}	HELO, MAIL, DATA, EOH, EOM	TLS session key size
{cipher}	HELO, MAIL, DATA, EOH, EOM	TLS cipher
{daemon_addr}	Always (Postfix ≥3.2)	Local server IP address
{daemon_name}	Always	value of milter_macro_daemon_name
{daemon_port}	Always (Postfix ≥3.2)	Local server TCP port
{mail_addr}	MAIL	Sender address
{mail_host}	MAIL (Postfix ≥ 2.6, only withsmtpd_milters)	Sender next-hop destination
{mail_mailer}	MAIL (Postfix ≥ 2.6, only withsmtpd_milters)	Sender mail delivery transport
{rcpt_addr}	RCPT	Recipient address  With rejected recipient: descriptive text
{rcpt_host}	RCPT (Postfix ≥ 2.6, only withsmtpd_milters)	Recipient next-hop destination  With rejected recipient: enhanced status code
{rcpt_mailer}	RCPT (Postfix ≥ 2.6, only withsmtpd_milters)	Recipient mail delivery transport  With rejected recipient: "error"
{tls_version}	HELO, MAIL, DATA, EOH, EOM	TLS protocol version
v	Always	value of milter_macro_v

postfix会在milter的不一样阶段发送指定的宏集合，这些宏集合与下表中的参数一块儿配置：

Postfix parameter	Milter protocol version	Milter protocol stage
milter_connect_macros	2 or higher	CONNECT
milter_helo_macros	2 or higher	HELO/EHLO
milter_mail_macros	2 or higher	MAIL FROM
milter_rcpt_macros	2 or higher	RCPT TO
milter_data_macros	4 or higher	DATA
milter_end_of_header_macros	6 or higher	EOH
milter_end_of_data_macros	2 or higher	EOM
milter_unknown_command_macros	3 or higher	unknown command

默认状况下，只有宏的值与main.cf,master.cf,smtp会话中或邮个投递事务中有不一样时才会被发送，若是须要强制发送宏，须要经过 milter_macro_defaults配置宏参数的默认值。能够设置成0，或更多的name=value对，甚至能够设置postfix所不识别的宏名称。