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CentOS 5.x | SendMail

I'd like to better understand how milter hand-offs work.

When a remote MTA initiates an SMTP session, my understanding is that Sendmail hands the message data off to the milter during that session. Where/how is this message data stored? Is this all done in memory? Or is there a "queue" area where message data for milter is stored for pickup by the milter?

If it helps, let's say I'm calling a milter like this:

INPUT_MAIL_FILTER(`foo', `S=unix:/var/lib/foo/foo.sock, F=T, T=C:5m;S:3m;R:5m;E:5m')dnl
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up vote 1 down vote accepted

It depends on the milter and what purpose it serves. For example MIMEDefang uses its own spool area in order to perform checks on the message body. Other milters do not maintain their own spool / queue and rely on the milter architecture and whatever sendmail hands them from its queue.

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