Description of problem:

I noticed that a particular procmail rule for my RH mail was failing,
but the mail was being correctly delivered my catchall mbox.

In postfix's main.cf I have:
mailbox_command = /usr/bin/procmail -f- -a "$USER"

fetchmail delivers my RH mail to local user 'mbooth', which has a
procmail rule which delivers it to a local user 'matthew'.

In my procmail log for 'matthew' I kept seeing:

procmail: Error while writing to "RedHat"
procmail: Truncated file to former size
procmail: Unlocking "RedHat.lock"
procmail: Locking "INBOX.lock"
procmail: Assigning "LASTFOLDER=INBOX"
procmail: Opening "INBOX"
procmail: Acquiring kernel-lock
procmail: Unlocking "INBOX.lock"
procmail: Notified comsat: "matthew@8894602:/home/matthew/mail/INBOX"
From mbooth.net  Sun Nov 23 12:16:59 2003
 Subject: weird procmail test 5
  Folder: INBOX                                                      
     2658

RedHat was 196MB. I moved a ton of it to an archive folder and with no
other modifications it is now correctly delivered.

Another weird thing is that if I did:

cat rh-test-mail | procmail -f- -a matthew

It worked, and was correctly delivered to the very large mbox. It was
only when called from postfix that the error occurred.

Version-Release number of selected component (if applicable):
procmail-3.22-9
postfix-2.0.11-4

How reproducible:

Always (for me).

Steps to Reproduce:
1. Create a really large mbox
2. Create a procmail rule to deliver mail to it
  
Actual results:

It fails

Expected results:

It doesn't fail :)

Additional info:

I've got a single big IDE disk. Filesystem is ext3 in LVM. Processor
is P42.4GHz with hyperthreading enabled.