Apple Computer’s Mail Disaster of 1991 87user, Mark E. Davis, is on the [email protected] mailing list, to dis-
cuss some alternatives to ASCII with the other members of that list.Sometime on Monday, he replied to a message that he received from
the mailing list. He composed a one paragraph comment on the orig-
inal message, and hit the “send” button.Somewhere in the process of that reply, either QuickMail or
MAIL*LINK SMTP mangled the “To:” field of the message.The important part is that the “To:” field contained exactly one “<”
character, without a matching “>” character. This minor point caused
the massive devastation, because it interacted with a bug in sendmail.Note that this syntax error in the “To:” field has nothing whatsoever
to do with the actual recipient list, which is handled separately, and
which, in this case, was perfectly correct.The message made it out of the Apple Engineering Network, and
over to Sun Microsystems, where it was exploded out to all the recip-
ients of the [email protected] mailing list.Sendmail, arguably the standard SMTP daemon and mailer for
UNIX, doesn’t like “To:” fields which are constructed as described.
What it does about this is the real problem: it sends an error message
back to the sender of the message, AND delivers the original mes-
sage onward to whatever specified destinations are listed in the recip-
ient list.This is deadly.The effect was that every sendmail daemon on every host which
touched the bad message sent an error message back to us about it. I
have often dreaded the possibility that one day, every host on the
Internet (all 400,000 of them^8 ) would try to send us a message, all at
once.On Monday, we got a taste of what that must be like.I don’t know how many people are on the [email protected] mailing
list, but I’ve heard from Postmasters in Sweden, Japan, Korea, Aus-(^8) There are now more than 2,000,000 hosts. —Eds.