For many of you, the mail loops which occurred last night and earlier
today resulted in temporary denial of service, as many of your mail
boxes overflowed and many of your service providers had problems
handling the volume. Our sincere apologies for the lost productivity.
For those who were merely minorly inconvenienced, our thanks for your
patience. I believe there was a specific circumstance which caused
the problem (details below).
The MIT postmasters are taking the appropriate actions on our end.
However, various bounce messages which were already queued up on
intermediate systems for delivery may still be delivered to you; we
cannot stop that, unfortunately.
Please do not send any further email to faq-maintainers@mit.edu
yourselves. The faq-maintainers mailing list has been discontinued
temporarily. It will either resume hosted at a third-party site or
hosted on majordomo on rtfm.mit.edu or rtfm.mit.edu's hardware
successor. When the new site is ready, all of you will be
individually informed and may re-subscribe at that time.
For those of you who like technical details or are just morbidly
curious, here's what I think happened.
----------------
| Any one who has maintained mailing lists with hundreds subscribers
| knows that no matter how careful you are at checking addresses
| before you subscribe somebody, inevitably dozens of mailing
| addresses become permanently invalid each month, and several of the
| addresses are temporarily out of service each day. Different mail
| delivery agents implement different "policies" about how and who to
| send notices of non-delivery (i.e., bounces) to. One of the most
| common policy is for the bounce message to be "From:
| MAILER-DAEMON@sitename" and sent to the SMTP envelope address of the
| original message.
|
| Many of you know that when you send a message to faq-maintainers,
| you will occasionally get some bounces back directly to you. This
| is a function of the fact that the MIT mail hubs leave the SMTP
| envelope address set to you, the sender of the message. It would be
| nicer if the SMTP envelope address was set to
| faq-maintainers-request@mit.edu so you the sender would not get
| bounces, but that would require special manually handling at the MIT
| mail hub end, which the MIT postmaster justifiably are not willing
| to do. (Nor would that have helped in this case, I note.)
|
| Some mail delivery agents are annoying broken, however. In
| particular, some take the message, parse out the Reply-to: or From:
| header (in the case of the summary I sent last night, that's
| "faq-maintainers@MIT.EDU"), and then send a message which is "To:"
| and "From:" that address, which doesn't make any semantic sense to
| me. What's worse, they ALSO set the SMTP envelope address to that
| address. In this case, the offending mailer is the one which was
| trying to deliver to the user "calon!oakacorn". Personally, I've
| seen these kinds of bounces before, but only in the context of
| trying to reply to *.answers submissions.
|
| So here's the deadly interaction when such a mailer gets involved
| with a list. My original message had these headers:
|
| From pshuang@nowhere.esd.sgi.com
| From: pshuang@MIT.EDU
| Reply-to: faq-maintainers@MIT.EDU
| To: faq-maintainers@MIT.EDU
|
| "Nicely" configured mail delivery agents initially were sending
| bounce messages that looked like this, which you folks didn't have to see:
|
| From {MAILER-DAEMON|etc}...
| From: {MAILER-DAEMON|postmaster|PMDF|etc}@...
| To: {owner-faq-maintainers@MIT.EDU|pshuang@nowhere.esd.sgi.com}
|
| However, the rogue agent sent a bounce message like this:
|
| From faq-maintainers@MIT.EDU
| From: faq-maintainers@MIT.EDU
| To: faq-maintainers@MIT.EDU
|
| Once that happened, all the normally-well-behaved mail delivery
| agents (following exactly the same rules as they were before)
| started sending bounce messages like this. (The rogue itself would
| have created a single mailer loop; the additional bounce messages from
| other agents simply multiplied the problem by starting up additional
| loops running simultaneously.)
|
| From {MAILER-DAEMON|etc}...
| From: {MAILER-DAEMON|postmaster|PMDF|...}@...
| To: faq-maintainers@MIT.EDU
|
| At least, that's the best I've been able to figure out. It didn't
| help much that the first time this happens to the mailing list was
| with a message which was quite so large, and thus filled out disk
| space very rapidly (600 copies and ~23MB in my mail spool).
|
| Switching to a real mailing list server should at least allow us to
| only permit subscribers to the list to send to the list; this would
| trap out the fact that the rogue mail delivery agent was using a
| "From:"/"From" address which is not a subscriber, and hence refuse
| that message. Turning on this feature has the disadvantage that
| people who use systems that do not make their "From:"/"From" lines
| consistent even if they are logged into different machines will have
| their messages to the list delayed until one of the list maintainers
| manually approves it. Hence even if this mailing list had been
| moved already to a real mailing list server, something like this
| particular meltdown could have occurred anyway, albeit at a slower
| pace (with one loop, not multiple loops).
----------------
== Ping Huang <faq-maintainers-request@mit.edu>
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