Re: Sendmail or Qmail ? ..
On Fri, Sep 05, 2003 at 03:14:09PM +1000, Russell Coker wrote:
> On Thu, 4 Sep 2003 22:58, Eric Sproul wrote:
> > First, scale is a consideration. Once we began to grow our customer
> > base, our email volume began to increase dramatically. Qmail queues
> > everything to disk, so the more mail you do, the more pressure you put
> > on your disk I/O. The server running Qmail was always blocking while it
> I was under the impression that Sendmail also queues everything to disk.
by default, it doesn't.
> How does it's queue operate then?
although it can be configured otherwise (either in the config file or in
command line options when calling /usr/sbin/sendmail), sendmail will first
attempt to deliver a message submitted to it, and will only fall back to
queuing it if the initial delivery fails. this is a performance disaster
because it makes resource limiting/rationing impossible, and is probably the
primary reason why a sendmail server will fall over and crash under a heavy
load that other MTAs (that implement a "queue everything first, deliver out of
the queue" approach) handle without breaking a sweat.
BTW, this is also one of the reasons why sendmail is slow with most list
managers - most of them do not call /usr/sbin/sendmail with '-O DeliveryMode=q'