Viktor Dukhovni via Postfix-users:
> On Fri, Dec 06, 2024 at 08:24:54AM +0000, Sad Clouds via Postfix-users wrote:
>
> > Hello, I agree with you, I'm just trying to see the big picture and how
> > all Postfix components fit together. At least for me, it helps to
> > visualize the entire Postfix architecture in one diagram, even if that
> > gets a bit messy.
>
> Note that in the smtpd->verify "pipeline" there is in fact no "anvil"
> between "smtpd" and "verify". The 'anvil' service is used as a simple
> query/response oracle, and subsequent processing does not flow through
> it.
>
> postscreen -> smtpd -> verify -> cleanup -> qmgr -> delivery-agent
> |^ ^ ^ /
> || \ \ /
> v| ---------------------/
> anvil
>
> rather the "probe message" part of the flow subsumes internal probe
> message generation, which naturally goes through "cleanup", because
> that's the only way that new messages enter the queue. Probe messages
> are special and delivery agents report the status of the probe (no
> actual message is actually delivered) to the "verify" service. This
> is quite similar to reporting of failures to the "bounce" service,
> but in this case success is also reported. The queue manager also
> receives a reply telling it that the delivery attempt is complete,
> and the probe can be removed.
>
> IIRC if the recipient address to be verified is a virtual alias, no
> probe is generated, and the address is treated as presumptively valid.
This is not a special case in Postfix. The cleanup_out_recipient()
function reports successful alias expansion through verify_append()
or trace_append() as needed.
Postfix address verification and delivery status notification have
similar implementations. They primarily differ in the back end that
they talk to (verify daemon versus bounce daemon). This similar
structure was easy to implement (unlike exim' callouts from the
SMTP server), and there have been very few problems with the
implementation.
Wietse
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