On Mon, Jun 28, 2010 at 11:33:49AM -0400, Jerry Feldman wrote:
>  I am considering the possibility of installing an iMap server at home,

It's not an apple product... it's IMAP =8^)

> First question, would maildir or mbox be the better mailbox format. 

It really depends on your usage patterns.  If you need to keep your
mail on NFS, you probably want maildir.  If you keep medium-to-large
folders and are in the habit of deleting and immediately expunging
after every deleted message, you probably want maildir.  Otherwise,
you'll probably find mbox performs better.  Maildir typically loses
(often by *A LOT*, depending on the underlying filesystem) when
opening large mailboxes, because mail messages are usually small, so
maildir does:

open -> read -> close -> seek -> open -> read -> close -> seek

where mbox does:

open -> read -> read -> read -> read -> close  (infrequent seeks so
  long as you have minimal fragmentation)

All those extra system calls really add up for large mailboxes.
Maildir also loses because on many filesystems, directories containing
many files are inherently slow to deal with.

Both of those factors can be mitigated with caching and choosing a
file system that optimizes for many small files; but even then, mbox
still usually wins by a little for most operations because it
eliminates the extra system calls (and mbox can benefit from caching
too).

> WRT mail formats. My preference would be maildir since there is never an
> issue with having to compact a mailbox in contrast to mbox.

That's one of the two major wins of maildir (the other being no
locking).  But, with some common usage patterns, that win can be a
very small win, resulting in a huge net loss.  Compaction (of mbox)
usually involves rewriting the entire mbox, which, if your mbox is
large, will be slow.  However, if you keep your inbox(es) small,
archiving mail you want to keep into another folder, then the time it
takes to do a compaction is negligible.  Note that changing message
attributes on mbox requires something similar to a compaction (unless
the program is smart enough to modify the message in place when
possible), but again, if you keep your inboxes small, this generally
doesn't matter.

In other words, in general, if you clean up your mail regularly, and
archive read mail, you almost certainly want mbox.  If you clean up
your mail sporadically, and don't separate archived mail from incoming
mail, then you probably want maildir.  If you keep all your mailboxes
small, and don't archive mail, then it doesn't make any difference,
unless locking is an issue for you.

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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