Permissions problem with mdbox maildir

[Emanuel Evans]

Hi! Apologies if this has come up before, or if this is a duplicate
posting (I tried posting before but I think it got lost). Anyways, I'm
trying to set up an IMAP server with dovecot, and everything seems to be
more or less working except that I periodically see error messages like
this in my logs:

  Feb 18 01:01:15 stark dovecot: lmtp(31956, root at aleme.nu): Error: link(/var/decrypted/vmail/aleme.nu/root/mailboxes/INBOX/dbox-Mails/dovecot.index, /var/decrypted/vmail/aleme.nu/root/mailboxes/INBOX/dbox-Mails/dovecot.index.backup.tmp) failed: Operation not permitted

I'm assuming it's a permissions problem with my maildir, but I can't
figure out what the relevant process is in order to fix it. The maildir
is owned by vmail with permissions set to 700; here is the output of
dovecot -n:

  # 2.1.7: /etc/dovecot/dovecot.conf
  # OS: Linux 3.2.0-4-amd64 x86_64 Debian 7.8 fuse.encfs
  mail_gid = vmail
  mail_location = mdbox:/var/decrypted/vmail/%d/%n
  mail_uid = vmail
  managesieve_notify_capability = mailto
  managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave
  namespace inbox {
    inbox = yes
    location = 
    mailbox Drafts {
      special_use = \Drafts
    }
    mailbox Junk {
      special_use = \Junk
    }
    mailbox Sent {
      special_use = \Sent
    }
    mailbox "Sent Messages" {
      special_use = \Sent
    }
    mailbox Trash {
      special_use = \Trash
    }
    prefix = 
  }
  passdb {
    args = /etc/dovecot/dovecot-sql.conf.ext
    driver = sql
  }
  plugin {
    antispam_allow_append_to_spam = no
    antispam_dspam_args = --user;root;deliver=;--source=error;--client
    antispam_spam = Junk
    antispam_trash = Trash
    sieve = ~/.dovecot.sieve
    sieve_before = /var/lib/dovecot/sieve/before
    sieve_dir = ~/sieve
    sieve_global_dir = /var/lib/dovecot/sieve/global
  }
  protocols = " imap lmtp sieve"
  service auth {
    unix_listener /var/spool/postfix/private/auth {
      group = postfix
      mode = 0660
      user = postfix
    }
  }
  service imap-login {
    inet_listener imaps {
      port = 993
      ssl = yes
    }
    service_count = 1
  }
  service lmtp {
    unix_listener /var/spool/postfix/private/dovecot-lmtp {
      group = postfix
      mode = 0600
      user = postfix
    }
    user = vmail
  }
  ... <ssl stuff> ...
  userdb {
    args = uid=vmail gid=vmail home=/var/vmail/%d/%n
    driver = static
  }
  protocol lmtp {
    mail_plugins = " sieve"
  }
  protocol imap {
    mail_plugins = " antispam"
  }

As you can see, I'm keeping the maildir on an encfs-encrypted volume, in
case that's relevant. Please let me know any ideas for why this might be
happening. Thanks in advance!

  Emanuel