[vchkpw] When I updated user's quota, maildirsize file is not with correct quota

[baby_moon]

For example:
  A user's quota is 1M, and some mails are in its Inbox, and I was checked
its directory, the maildirsize file is there.
  When I changed this user's quota to 3M, after a mail come in, the
quota's total number is same as before. Who knows how to solve this
problem?