howto auto create user mailbox ?

[JOYDEEP]

Dear llist,

I am a newbie in cyrus-imap server technology. I am using
cyrus-imapd-2.2.12-5.
the map server is running well. regarding user inbox I have to create it
by using cyradm tool as cyrus admin user.
But I like such an arrangement where user mail box can be created
automatically when user successfully log into cyrus.

how can I achieve this ? what may be the configuration of imapd.conf ?
thanks.