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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.Hawaii.Edu!news.uoregon.edu!arclight.uoregon.edu!mr.net!visi.com!uunet!in2.uu.net!128.248.178.247!koobera.math.uic.edu!djb From: djb@koobera.math.uic.edu (D. J. Bernstein) Message-ID: <1996Dec1504.00.21.25291@koobera.math.uic.edu> Date: 15 Dec 1996 04:00:21 GMT Newsgroups: comp.mail.sendmail,comp.mail.smail,comp.unix.bsd.freebsd.misc Subject: Re: sendmail vs. qmail References: <57tf61$gq7@raven.eva.net> <1996Dec1005.15.53.2968@koobera.math.uic.edu> <SHALUNOV.96Dec13131524@math.wisc.edu> <58vgks$332@nntp1.best.com> Organization: IR Lines: 32 Xref: euryale.cc.adfa.oz.au comp.mail.sendmail:35204 comp.mail.smail:2715 comp.unix.bsd.freebsd.misc:32626 Matt Dillon <dillon@flea.best.net> wrote: > You create a potential failure mode in your mail system Nope. The system is protected by a concurrency limit---20 by default, configurable up to 255. In contrast, any big burst of mail will cause sendmail to chew up all your memory and start thrashing. The load average limit simply doesn't kick in quickly enough. Kyle Jones observed this at UUNET a long time ago and had to write code to deal with it. (Even worse, when the load average limit does kick in, sendmail delays mail until the next queue run. Sometimes a few pieces of mail are repeatedly unlucky and end up being delayed for hours.) sendmail also fails when the queue gets too big. When AOL went down, one qmail host was reported happily dealing with a 2000-message queue, while sendmail hosts were dying left and right with smaller queues. See issues 18.30 and 18.31 of the RISKS Digest. > the best solution is to have no failure modes at all Unfortunately, even with an MTA that keeps running 24x7, there's a limit to how many deliveries you can perform in a day. You won't be able to sustain a daily load higher than that. Fortunately, qmail can do a _lot_ of deliveries per day. The #2 LISTSERV host recently outgrew sendmail at about half a million deliveries a day; now it's running qmail. ---Dan Put an end to unauthorized mail relaying. http://pobox.com/~djb/qmail.html