[Mailman-Users] Query about low-level SMTP errors

Steve Burling srb at umich.edu
Fri Sep 28 15:44:48 CEST 2007

This is really an "is my understanding correct" question...

Our mail server is getting the snot beat out of it by spambots, and even 
though I've turned on pretty aggressive connection rate control and 
limiting of the number of concurrent connections from any particular bot, 
we still occasionally hit sendmail's (configured) limit of 70 child 
processes, at which point we start refusing connections for awhile.  During 
those times, mailman is also refused connections, resulting in errors like 
this from smtp-failure:

Log file: smtp-failure
     23 delivery failed with code -1: (111, 'Connection refused')
      1 Low level smtp error: (111, 'Connection refused'), msgid: 
<mailman.9.1190894402.11108.some-list at icpsr.umich.edu>
      1 Low level smtp error: (111, 'Connection refused'), msgid: 
<mailman.8.1190894402.11108.some-other-list at icpsr.umich.edu>

Am I correct that Mailman doesn't consider these permanent errors, and will 
re-try these attempts later?  Nothing seems to be left lying around in the 
queue files, so I'm hoping that subsequent retries succeeded, and not that 
Mailman just gave up and tossed things.  (That doesn't seem likely to me, 
but I figured it was better to ask, so I know if I have to spend more time 
trying to figure out how to make sendmail only refuse connections on the 
non-localhost interface.  Although if anyone knows the magic knob to do 
that, I would appreciate a hint.)

Steve Burling                                    <mailto:srb at umich.edu>
University of Michigan, ICPSR                    Voice: +1 734 615.3779
330 Packard Street                               FAX:   +1 734 647.8700
Ann Arbor, MI 48104-2910

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