dovecot - Sep 2006 - Dovecot behaviour when the server's file system fails (possible feature request)

I've met a couple of times a situation, that there is something
wrong with the mail server's operating system / file system,
but Dovecot is still working, although it cannot any more
access the mailbox files. The result is, that the imap mail
client in the workstation automatically synchronises with
the improperly empty-looking mailbox, effectively deleting
everything previously loaded into the workstation's mail
client (eg. Outlook Express) when using imap protocol.

This is very annoying, especially when the workstation isn't
connected with a high-speed-enough connection, since after
the server is properly brought up again, reloading all the
contents of the improperly emptied mail client may take
considerable amount of time. This is especially the case, if the
workstation has kind of mobile connection (eg. gprs) with
very limited bandwith -in that case the sychronizing of eg.
20MB account may take at least from half an hour to more
than one hour, and in some cases (eg. gprs roaming) also
cost considerable amount of money (gprs data transfer may
cost from eg. 5 to over 10 euros or dollars per megabyte,
when roaming outside the phone operator's own network).

So, is there currently a way to configure Dovecot in a way
it would recognize that the mailbox actually is not accessible,
and in that case it would return an error message to the mail
client instead of returning "empty mailbox"? Of course, a
smart enough mail client might also ask something from the
user, but that seems not be the case either...


If this behavious cannot be changed with the current
configuration options, then a kind feature request to the
developer:
Would it be possible to change the behaviour of Dovecot
when it actually can not access the mailbox files?

Although the actual problem in this case is outside Dovecot,
this kind of improvement would greatly improve the error
tolerance of the whole system.

--
TiN

On Sun, 2006-09-03 at 13:25 +0300, Timo Neuvonen wrote:
> I've met a couple of times a situation, that there is something
> wrong with the mail server's operating system / file system,
> but Dovecot is still working, although it cannot any more
> access the mailbox files.
..
> So, is there currently a way to configure Dovecot in a way
> it would recognize that the mailbox actually is not accessible,
> and in that case it would return an error message to the mail
> client instead of returning "empty mailbox"? Of course, a
> smart enough mail client might also ask something from the
> user, but that seems not be the case either...
How would Dovecot figure out if the mailbox isn't accessible because of
some filesystem error, or because it's simply a new user who doesn't yet
have a mailbox?

If any system calls return eg. EIO errors Dovecot catches those and fail
with internal error messages. So I guess in your case everything seemed
to work, but the mail directories just were lost. I can't think of how
Dovecot could in a generic way detect that this is the case.
> If this behavious cannot be changed with the current
> configuration options, then a kind feature request to the
> developer:
> Would it be possible to change the behaviour of Dovecot
> when it actually can not access the mailbox files?
Change mail_executable to point to a script:

#!/bin/sh

if [ ! -f ~/mail ]; then
  echo "* BAD mails are lost, bye"
  exit 0
fi
exec /usr/local/libexec/dovecot/imap

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