Stefan Paletta writes:
> Sam wrote/schrieb/scribsit:
> > different domains will result in only 5,000 DNS queries. Meanwhile, each
> > instance of qmail-remote should diligently issue a DNS query - for a
> > grand sum of 10,000 queries overall.
>
> When we're talking about lists of that size, you will for sure have
> the resources to handle 5000, 10000 or 100000 DNS queries compared to
> the resources you need for actually sending the messages.
>
> My experiences show, that for lists of up to 10000 recipients, qmail
> will already have finished lots of deliveries when the first lookups
> on bad/unreachable addresses get a timeout. With serialized lookups
> everything will just sit idle for ages.
>
> I all boils down, as you said in another mail, to that qmail
> opimizes for delivery time and optimizes bandwidth usage at the upper
> end.
Well, I wouldn't say that. Not exactly. Qmail optimizes delivery time,
and requires reasonable (but not too great) bandwidth in situations
involving medium to moderately high volumes of mail. Qmail will also do
pretty well when the mail volume is low, although there are certain
pathological situations where Qmail will fail miserably with low mail
volume. Also, Qmail will do poorly in the extreme upper end of the range,
where your mail volume goes through the roof. That's mostly a result due
to a combination of factors: namely excessive amounts of DNS queries, and a
lot of excessive TCP/IP traffic because Qmail does not recycle TCP/IP
connections, nor does it batch same-domain recipients in any way. Also,
the fact that its limited to 255 concurrent qmail-remotes also comes into
play, at one point. Sure, you can argue that all you have to do is to put
in a dozen of OC-3s to handle the excessive amounts of bandwidth, and solve
the 255 qmail-remote issue by instead splitting the mail traffic across
multiple servers, in parallel. However, multiple servers still adds up to
the same amount of bandwidth via your pipes, and no amount of bandwidth
will affect the fact that a few hops away, most your traffic gets squeezed
through a single T-1, or even a T-3.
--
Sam
