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Re: Upgrade a mail server

On Mon, Feb 18, 2002 at 06:02:38PM -0600, Rich Puhek wrote:
> Craig Sanders wrote:
> > i'd love to convert it over to Maildir/ but haven't yet found any way
> > that doesn't involve many hours of downtime while converting the
> > mailboxes from mbox format to Maildir.
> > 
> > one of these days i'll have the time to sit down and work out a good
> > solution to the problem.  i've got some ideas but no time to work them
> > out.
> Look at qmail's site. They've got some nice tools for scripting the
> switch. Some will need a little bit of cooking for your specific
> implementaion, but basicly it's there.

yes, i've seen all that.

none of the available scripts do the job in what i consider to be a safe
manner while the system is STILL RUNNING as a mail server (handling both
incoming mail AND pop & imap connections from hundreds of users).

> Downtime will be the time it takes to install procmail (or other
> Maildir happy LDA) and restart sendmail (assuming home directories are
> setup properly.) Also need to restart your POP3 daemon of course.
> Then, you can fire off a script to convert the mailboxes.

no, there is a LOT more to it than that...and the fact that NONE of the
existing conversion scripts take that into account is why i don't
consider any of them safe enough to use as is.

you might want to risk it on a home system with only a few dozen
accounts or less, but nobody in their right mind would convert a
professional mail server with thousands of accounts without first
planning out every step of the transition and taking the time to think
of (and work around) every little thing that *could* go wrong.

end-users care about their mail, and any fault with the mail system is
highly-visible....they WILL call the helpdesk if they can't get their

there are several race-conditions which must be avoided, and oddities
that WILL cause users to call the helpdesk and whine that they can't
read their mail (e.g. when the pop daemon is Maildir/ but their mailbox
hasn't been converted yet because it takes a long time  to convert
several gigabytes of other users mbox files to maildir.  users will not
tolerate being unable to access their mail for an hour, let alone a day
or several days)

the problem isn't unsolvable.  it's just tedious to get it right.  i've
already mapped out ways around these problems (*) - or at least the
problems that i've thought of - one of these days when i get the time
i'll implement it on a test system, and then run it on my real system
when it is working to my satisfaction.

in short: if you plan the transition right then the users won't even
notice that you've changed anything, it will all happen seamlessly
behind the scenes.   if you don't plan it properly then your helpdesk
will be overloaded with calls about mail problems.

(*) it involves using semaphore files in each users homedir to indicate
whether they are maildir or still mbox, plus procmail/maildrop rules to
deliver accordingly, and a pop proxy which chooses whether to connect to
the mbox or Maildir capable pop daemon.  when that's done it is possible
to safely convert all the mboxes to maildirs


craig sanders <cas@taz.net.au>

Fabricati Diem, PVNC.
 -- motto of the Ankh-Morpork City Watch

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