On Mon, 12 Apr 1999, Keith Burdis wrote:
> > qmail is great that way at inflicting remote DoS attacks against other
> > mailers.
>
> Well, the obvious question is why do mailers accept connections that they
> cannot handle? If the remote host accepts the mail it should be prepared to
> deal with it.
blah blah blah.
I don't know? Why does "qmail" accept connections that it cannot handle?
It is a pretty simple concept: even if a mailer can "handle" it, if you
send 1 simultaneous bit of mail to 1 machine, while using all your other
slots for sending to other machines, you will get x% of each machine's
resources. If you send 120 simultaneous messages, then you only get y% of
the machine's resources, where y is between a little (eg. if the machine
normally has 10000 incoming connections) to a huge amount (eg. if the
machine normally has 2 incoming connections) less than x.
Because of somewhat nonsensical hard coded limits, when sending a lot of
outbound mail with qmail, the number of simultaneous connections open
total often is a big limitation. Because of that, the fastest way to send
mail is to ensure you aren't overloading any remote machine more than
necessary at any given time, so that each connection to that machine takes
the least time possible, even if that involves more seialization.
Trying to blame the remote mailer for qmail's less than great behaviour in
this area is silly.
