In my posting to LSTOWN-L of 19 Jun with a subject: Overview:
Electronic Mail Delivery, I identified 9 typical areas that
affect electronic mail delivery.  The fact that e-mail gets
delivered at all sometimes makes me think that that is a miracle
of modern communications.  There are so many fingers in the
electronic e-mail pie constantly fiddling with it.  Nothing
hardly ever stays the same: software/hardware are updated,
sysadmins and users come and go, mail-boxes fill, people
make mistakes, one change impinges somewhere else, natural
disasters, router outages (could affect host name lookups),
and the list goes on.
 
As postmaster, I just received 26 bounces from another PSU.EDU
site for mail sent to that administrative e-mail system.  WHY?
Because the sysadmin had gone on vacation and was the only one
who knew how to restart their system which has been "down" for
3 days.
 
/Pete Weiss,
 Penn State