[5254] in Kerberos
Re: MAIL LOOP: kerberos IV installation problem
daemon@ATHENA.MIT.EDU (Dennis Glatting)
Wed May 24 01:47:59 1995
Date: Tue, 23 May 1995 22:36:56 -0700
From: Dennis Glatting <dennisg@CyberSAFE.COM>
To: ramus@nersc.gov (Joe Ramus)
Cc: kerberos@MIT.EDU
Reply-To: dpg@CyberSAFE.COM
> Date: Tue, 23 May 95 18:10:49 PDT
> From: ramus@nersc.gov (Joe Ramus)
>
> Are other people getting repeated empty messages as
> shown below? I have received this about 25 times now.
>
> The message headers indicate that the repeated message originates
> at info.elf.stuba.sk which keeps sending it to MIT.
>
Having inflicted a similar annoyance I'll tell you what I
learned. The Kerberos list is tied to a database. When a
message is sent to kerberos@mit.edu the MIT mailer
queries the database to expand the list. The MIT mailer
assumes the sender's SMTP connection will not time-out
during the expansion. Bad assumption. Although SMTP
time-outs use to be infinite, RFC-1123 (I believe)
changed that. Some SMTP time-outs are now as low as ten
minutes. Berkeley sendmail 8.6.x uses the RFC-1123
recommended values.
The scenario works like this. Someone sends a message to
kerberos@mit.edu. The MIT mailer holds the SMTP
connection while it expands the list. Ten minutes pass, a
time-out. The sender closes the connection. The MIT
mailer continues message processing. The sender's next
mail queue interval elapses (fifteen to sixty minutes).
The sender's mailer discovers an undelivered message in
its queue. Let me tell you from personal experience,
sendmail can be relentless!
The bottom line is that anyone who sends mail to
kerberos@mit.edu must lengthen their SMTP time-outs or
risk the embarrassment of having their mailer repeat
the message every queue interval.
-dpg
