Patrik Rak:
> > If we want to address the real problem: slow or non-responding DNS
> > and SMTP servers, then we should not waste an entire SMTP client
> > process blocking on DNS lookup and TCP connection handshake in the
> > first place. Instead it is more efficient to interpose a prescreen(8)
> > process between the qmgr(8) and smtp(8) processes. This process
> > can look up DNS, create the initial TCP connection, peek() at the
> > remote server greeting, and keep the bogons away without wasting
> > any smtp(8) processes. Just like postscreen(8) can keep bogus SMTP
> > clients away without wasting smtpd(8) processes.
>
> Hmm, this is definitely an interesting idea. Looks pretty cool. But
> there are few problems as I see it:
>
> First, it seems to work when the servers you talk to are slow, you can
> talk to thousands of them at the same time easily. But what happens if
> you initiate thousands of connections but then you find out that the
> servers do not respond slowly, but are actually pretty fast? You still
I am not that stupid. Just like postscreen(8) handles up a LIMITED
number of connections at any point in time, so would prescreen(8)
handle only a limited number of delivery requests at any point in
time, giving back pressure to qmgr(8).
The main benefit is that presecreen(8) parallizes the waiting
for DNS lookup, TCP handshake, and server greeting.
Wietse
