How to Configure Cyrus-Imap to create mailbox Automatically.
Auto create mailbox
Add the below mentioned lines in the /etc/imapd.conf
autocreatequota: 20480
unixhierarchysep: yes
quotawarn: 90
autocreateinboxfolders: Drafts|Sent|Trash
autosubscribeinboxfolders: Drafts|Sent|Trash
lmtp_over_quota_perm_failure: 1
This will create 20MB mailboxes automatically during the first login of the user.