RE: Activation points and callout modes

On Wed, 2 Feb 2005, The Purple Streak, Hilarie Orman wrote:
>
> For the SMTP queues, it had seemed an interesting possibility to have
> the callout server maintain the queues.  That's a radical change to
> the normal SMTP implementation, admittedly, and it might not make
> sense from the perspective of I/O efficiency.  But it would facilitate
> a very lean SMTP implementation.

Existing callout protocols try to avoid any queueing in the policy server.

Postfix has support for a pre-reception SMTP proxy, effectively mode 1 but
implemented like mode 4.
http://www.postfix.org/SMTPD_PROXY_README.html

It also has a simpler policy protocol, which is more like an OPES mode 1
callout protocol.
http://www.postfix.org/SMTPD_POLICY_README.html

The Sendmail milter protocol is another mode 1 example, but it's defined
by its implementation rather than in an open fashion.
http://www.milter.org/milter_api/

Tony.
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