Julian Mehnle writes:
Sam Varshavchik wrote:The strategy in [draft-varshavchik-exdata-smtpext] has been in Courier for years.
Courier has an internal API for recipient-specific content filters. If enabled, Courier will begin behaving exactly as that document describes.
How can this be enabled?
man localmailfilter
To what extent does the courierfilter API support it?
It doesn't. This is a different API.
How would a courierfilter know whether the SMTP transaction in progress uses the EXDATA extension, etc.?
It doesn't. The courierfilter mechanism is not invoked at all.
It's based on a subset of maildrop's filtering language, and uses maildrop. A bunch of special files, with special permissions, are installed in a few special places. The files contain a maildrop filtering recipe, except for a few statements that are banned (to, cc, xfilter, and few others). These files are owned by each mail account. A RCPT TO:<[EMAIL PROTECTED]> reads mailbox's special file, if it exists. The maildrop recipe has access to the connecting IP address and the return address, from MAIL FROM. The exit code from maildrop determines what Courier does with the RCPT TO: statement.
When the message's contents are received, but before Courier replies to the DATA command, Courier goes over all local mailboxes and runs another maildrop filter recipe, for the DATA command, which now has access to the entire message. The results from each mailbox are assembled into an EXDATA-formatted reply.
The draft also describes, exactly, what to do with mailing list traffic. It really describes what Courier's been doing, for quite some time.
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