[Dovecot] "failed to store into mailbox 'INBOX': Not enough disk space." with large mail

[Johannes Dröge]

Hello,

I am having this error message on some rare emails with more than 6 mb 
or so. Neither the dovecot server nor the filesystem where the maildir 
resides have any quota or are full at the time of delivering.

The mails goes getmail->postfix->dovecot delivery agent

Is the mail written to any other place than the maildir folder? Even 
though all my temp folders should also be able to hold some megabytes...

Thanks for any help,
Johannes

message:
*sieve: info: started log at ...
error: msgid=<XXX>: failed to store into mailbox 'INBOX': Not enough 
disk space.
*
dovecot --version
1.2.10

dovecot -n
# 1.2.10: /etc/dovecot/dovecot.conf
# OS: Linux 2.6.26-2-686 i686 Debian 5.0.4 xfs
log_timestamp: %Y-%m-%d %H:%M:%S
protocols: imaps
ssl_cert_file: /etc/certificates/XXX
ssl_key_file: /etc/certificates/XXX
login_dir: /var/run/dovecot/login
login_executable: /usr/lib/dovecot/imap-login
login_greeting: XXX
mail_access_groups: mail
mail_location: maildir:/services/mail/%u
mbox_write_locks: fcntl dotlock
lda:
   postmaster_address: root
   mail_plugins: sieve
auth default:
   verbose: yes
   passdb:
     driver: pam
   userdb:
     driver: passwd
plugin:
   sieve: /var/sieve-scripts/%u/filter.sieve