I currently have a 2Gb personal maildir quota, and I'm currently using
1Gb. I use IMAP. Full IMAP subfolder queries ("check all folders for
new mail", etc...) are a CPU hog for large mailboxes, and changing your
filesystem isn't going to help that much. For those of you familiar
with Big-O notation, I believe it's a O(N) operation for the number
of folders under your INBOX. If it's too slow, get a bigger CPU, or
more of them (think cluster).
I had the same problem: a mailbox with 260.000 messages that killed the server
when opened in IMAP. I use RH with ext3.
I made some tests formatting a partition with Reiserfs (3) under Linux RH 9 and
moving the maildir there.
There is no a real increase in performance from ext3 to Reiserfs when you
handle such maildirs.
Better looking for a faster disk or a faster machine.
Dedicated Mail Servers