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Re: mailutils

From: Nic Ferrier
Subject: Re: mailutils
Date: 11 Mar 2002 23:49:09 +0000

xystrus <address@hidden> writes:

> Well, we discussed this at length on the mutt users list. 
> Maildir is not without its own problems...  It takes 
> substantially longer to open and index a Maildir/MH folder 
> than it does to do the same for a MBOX folder.  

This is an interesting paper about maildir:


I happen to agree with it, but it's interesting whatever your

> > Appending mail is easy, but how about to 
> > remove message 501 and 60 in a mailbox that 
> > contains 2000 msgs.  
> IIRC from reviewing IMAP4 before, it doesn't allow for this... 

Yes it does.

> but what I had in mind for this is to expunge only on mailbox 
> close, and have the server fork a backround process to do this 
> so that the user can continue to deal with mail in a different 
> folder.  

The trouble with that is that it's not what the IMAP spec says should
happen and it's not what the user expects either. The user expects
expunge to be done when they ask for it.

> > What happen when something goes wrong? 
> > Say you ran out of disk space? or Quotas? 
> How does using Maildir help these problems?  I think they  
> actually make it *worse*, as each message now takes up at  
> least one full disk block, no matter how much data is in it. 
> The exception is if you're using a filesystem like ReiserFS 
> which is designed to deal with this by packing data from 
> multiple files into one disk block... 

But you can't split a single file across multiple discs, if I get a
really big maildir my imap server *could* start linking in other
storage resources.

You do seem to have missed the biggest scaling problem with
maildir. The biggest problem is that inodes tend to run out on you
with conventional file systems.

I was the architecht for one of the big european free email systems,
we started out using maildir for imap but it quickly became apparent
that we wouldn't be able to do it efficiently because the file usage
of mail is so high (lot's of small messages). We switched to mbox.

If I were doing it now I'd probably use ReiserFS on Linux, I'm
planning to try that for a new mail service I'm setting up.

The big problem with imap and mbox of course is locking. You might
think that isn't a problem because the imap server is a closed
system, but it isn't quite, not if it implements shared
folders. Without shared folders then the locking problem almost goes

Nic Ferrier
(who wishes he had the time to add maildir support to the gnu imap

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