sendmail, 4th Edition

The InputMailFilters Option

Filters to connect to for processing messages through external programs are declared with the X configuration command (The X Configuration Command on page 1173). One form of that command (for use in your mc file) not only declares the Milter, but also defines the order in which the Milters will be called:

INPUT_MAIL_FILTER(`progA', ``S=local:/var/run/f1.sock, F=R'')
INPUT_MAIL_FILTER(`progB', ``S=inet6:999@localhost, F=T, T=S:1s;R:1s;E:5m'')

Here, the Milters will be called in the order progA first and progB second, for each phase of the message. Table 26-5 shows which portion of the message is checked by each Milter in time order. Note the change in order when the DATA phase begins (header/body).

Table 26-5. Milters called in time order

Milter	Screens what
progA	Connection information, such as hostname and IP address
progB	Connection information, such as hostname and IP address
progA	HELO/EHLO greeting information
progB	HELO/EHLO greeting information
progA	MAIL From: address and ESMTP arguments
progB	MAIL From: address and ESMTP arguments
progA	RCPT To: address and ESMTP arguments
progB	RCPT To: address and ESMTP arguments
progA	DATA command (V8.14 and later)
progB	DATA command (V8.14 and later)
progA	The message headers
progA	The message body
progA	The end of a message (a semaphore)
progB	The message headers
progB	The message body
progB	The end of a message (a semaphore)

Each Milter is handed portions of a message envelope ...