[H-GEN] Humbug machine problems and lost email

[Bruce Campbell]

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On Tue, 24 Sep 2002, Greg Black wrote:

> Robert Brockway wrote:
>
> | On Tue, 24 Sep 2002, Greg Black wrote:
> |
> | > The point of my message is that this has not happened.  Messages
> | > that were sent to gjb at humbug.org.au have not been delivered
> | > (yet).  I am wondering if they ever will.
> |
> | Right now I'm not up on the exact details of the outage but if there was a
> | hardware problem any messages on disk at the time of the crash may have
> | bitten the bullet :( This is conjecture only though.
>
> This seems like a long shot.  In general, a message makes its
> way through various hosts until it reaches its destination.  In
> this case, the destination host sees that the message is now to
> be sent elsewhere and does so immediately.  So, unless the crash
> happens in that couple of seconds, the message should not be
> lost.

Well, not really.  Any MTA worth its salt only acknowledges successful
receipt of a message to the sending host after it has successfully written
the message to its spool directory.  If you have a slowly failing hard
drive returning inconsistent information, the MTA may well think that the
message has been successfully written, but when it comes to process the
message (ie, forward it on), it suddenly cannot find it.

Hence, if the crash occurs over a period of hours, your MTA might be
accepting messages (and complaining bitterly in its log files that its
spool directory is now inconsistent) effectively into a black hole.

diskcheckd(8) is your friend.
http://www.freebsd.org/cgi/man.cgi?query=diskcheckd&apropos=0&sektion=8&manpath=FreeBSD+Ports&format=html

> | I knew you'd be up on the mail routing Greg, but I figured others on the
> | list would like to know what was happening.
>
> Yes, this might even provide some useful clues about mail
> routing and general message handling.  I don't actually care
> about the lost messages in this case -- but I do like to know
> what happens to email that doesn't get to its intended target.

If a given message hasn't arrived at its destination, or been returned to
the nominated sender within the de-facto default (pretty much 7 days
thanks to Sendmail), it has effectively vanished from this world, and
there really isn't anyone that you can try to claim insurance from (unlike
regular mail, most email doesn't have a reliable 'registered post' option
;) ).

Sometimes it gets picked out of old backups weeks/months/years later, or
Admins (in trying to fix another problem) shift the active spool elsewhere
and don't put it back for a few weeks (nothing any large QLD university
would ever do, I'm sure) and it reappears, but in general, if it doesn't
arrive after the above time, its gone.

Usually when a large relay host suffers a serious failure, the naturally
responsible admins try to provide a more-than-best-effort in ensuring that
the mail continues on its way.  In some cases, this is just not possible
;(.

--==--
Bruce.



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